Java Programming NOTES1

UNIT-1
OOP Concepts
Object Oriented Programming is a paradigm that provides many concepts such as inheritance,
data binding, polymorphism etc.
Simula is considered as the first object-oriented programming language. The programming

paradigm where everything is represented as an object is known as truly object-oriented
programming language.
Smalltalk is considered as the first truly object-oriented programming language.
OOPs (Object Oriented Programming System)
Object means a real word entity such as pen, chair, table etc. Object-Oriented Programming is
a methodology or paradigm to design a program using classes and objects. It simplifies the
software development and maintenance by providing some concepts:
o Object
o Class
o Inheritance
o Polymorphism
o Abstraction
o Encapsulation
Object
Any entity that has state and behavior is known as an object. For example: chair, pen, table,
keyboard, bike etc. It can be physical and logical.
Class
Collection of objects is called class. It is a logical entity.
Inheritance
When one object acquires all the properties and behaviours of parent object i.e. known as
inheritance. It provides code reusability. It is used to achieve runtime polymorphism.
JAVA PROGRAMMING PAGE 1
Polymorphism
When one task is performed by different ways i.e. known as polymorphism. For example: to
convince the customer differently, to draw something e.g. shape or rectangle etc.
In java, we use method overloading and method overriding to achieve polymorphism.
Another example can be to speak something e.g. cat speaks meaw, dog barks woof etc.
Abstraction
Hiding internal details and showing functionality is known as abstraction. For example: phone
call, we don't know the internal processing.
In java, we use abstract class and interface to achieve abstraction.
Encapsulation
Binding (or wrapping) code and data together into a single unit is known as encapsulation.
For example: capsule, it is wrapped with different medicines.
A java class is the example of encapsulation. Java bean is the fully encapsulated class because all
the data members are private here.
Benefits of Inheritance
 One of the key benefits of inheritance is to minimize the amount of duplicate code in an
application by sharing common code amongst several subclasses. Where equivalent code
exists in two related classes, the hierarchy can usually be refactored to move the common
code up to a mutual superclass. This also tends to result in a better organization of code
and smaller, simpler compilation units.
 Inheritance can also make application code more flexible to change because classes that
inherit from a common superclass can be used interchangeably. If the return type of a
method is superclass
 Reusability - facility to use public methods of base class without rewriting the same.
 Extensibility - extending the base class logic as per business logic of the derived class.

 Data hiding - base class can decide to keep some data private so that it cannot be
altered by the derived class
Procedural and object oriented programming paradigms

Java Programming- History of Java
The history of java starts from Green Team. Java team members (also known as
Green Team), initiated a revolutionary task to develop a language for digital
devices such as set-top boxes, televisions etc.
For the green team members, it was an advance concept at that time. But, it was
suited for internet programming. Later, Java technology as incorporated by
Netscape.
Currently, Java is used in internet programming, mobile devices, games, e-business

solutions etc. There are given the major points that describes the history of java.
1) James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java
language project in June 1991. The small team of sun engineers called Green
Team.
2) Originally designed for small, embedded systems in electronic appliances like set-
top boxes.
3) Firstly, it was called "Greentalk" by James Gosling and file extension was .gt.
4) After that, it was called Oak and was developed as a part of the Green
project.
Java Version History
There are many java versions that has been released. Current stable release of Java
is Java SE 8.
1. JDK Alpha and Beta (1995)

2. JDK 1.0 (23rd Jan, 1996)
3. JDK 1.1 (19th Feb, 1997)
4. J2SE 1.2 (8th Dec, 1998)
5. J2SE 1.3 (8th May, 2000)
6. J2SE 1.4 (6th Feb, 2002)
7. J2SE 5.0 (30th Sep, 2004)
8. Java SE 6 (11th Dec, 2006)
9. Java SE 7 (28th July, 2011)
10.Java SE 8 (18th March, 2014)
11.Java SE9 (July 27, 2017)

Features of Java
There is given many features of java. They are also known as java buzzwords. The Java
Features given below are simple and easy to understand.
1. Simple
2. Object-Oriented
3. Portable
4. Platform independent
5. Secured
6. Robust
7. Architecture neutral
8. Dynamic
9. Interpreted
10. High Performance
11. Multithreaded
12.Distributed
Java Comments
The java comments are statements that are not executed by the compiler and interpreter. The
comments can be used to provide information or explanation about the variable, method, class or
any statement. It can also be used to hide program code for specific time.
Types of Java Comments
There are 3 types of comments in java.
1. Single Line Comment

2. Multi Line Comment
3. Documentation Comment
Java Single Line Comment
The single line comment is used to comment only one line.
Syntax:
1. //This is single line comment

Example:
public class CommentExample1 {

public static void main(String[] args) {
int i=10;//Here, i is a variable
System.out.println(i);
}
}
Output:
10
Java Multi Line Comment
The multi line comment is used to comment multiple lines of code.
Syntax:
/*
This
is
multi line
comment
*/
Example:
public class CommentExample2 {

/* Let's declare and
print variable in java. */
int i=10;
System.out.println(i);
} }
Output:
10

Java Documentation Comment
The documentation comment is used to create documentation API. To create documentation API, you need
to use javadoc tool.
Syntax:
/**
This
is
documentation
comment
*/
Example:
/** The Calculator class provides methods to get addition and subtraction of given 2
numbers.*/ public class Calculator {
/** The add() method returns addition of given numbers.*/
public static int add(int a, int b){return a+b;}
/** The sub() method returns subtraction of given
numbers.*/ public static int sub(int a, int b){return a-b;} }
Compile it by javac tool:
javac Calculator.java
Create Documentation API by javadoc tool:
javadoc Calculator.java
Now, there will be HTML files created for your Calculator class in the current directory. Open the HTML
files and see the explanation of Calculator class provided through documentation comment.

Data Types
Data types represent the different values to be stored in the variable. In java, there are two types of data types:
o Primitive data types

o Non-primitive data types
Data Type Default Value Default size
boolean False 1 bit
char '\u0000' 2 byte
byte 0 1 byte
short 0 2 byte
int 0 4 byte
long 0L 8 byte
float 0.0f 4 byte
double 0.0d 8 byte
Java Variable Example: Add Two Numbers

class Simple{
public static void main(String[] args){
int a=10;
int b=10;
int c=a+b;
System.out.println(c);
}}
Output:20

Variables and Data Types in Java
Variable is a name of memory location. There are three types of variables in java: local, instance
and static.
There are two types of data types in java: primitive and non-primitive.
Types of Variable
There are three types of variables in java:
o local variable
o instance variable
o static variable
1)Local Variable
A variable which is declared inside the method is called local variable.
2) Instance Variable
A variable which is declared inside the class but outside the method, is called instance variable . It
is not declared as static.
3) Static variable
A variable that is declared as static is called static variable. It cannot be local.
We will have detailed learning of these variables in next chapters.
Example to understand the types of variables in java
class A{
int data=50;//instance variable
static int m=100;//static variable
void method(){
int n=90;//local variable
}
}//end of class
Constants in Java
A constant is a variable which cannot have its value changed after declaration. It uses the 'final'
keyword.
Syntax
modifier final dataType variableName = value; //global constant
modifier static final dataType variableName = value; //constant within a c

Scope and Life Time of Variables
The scope of a variable defines the section of the code in which the variable is visible. As a
general rule, variables that are defined within a block are not accessible outside that block.
The lifetime of a variable refers to how long the variable exists before it is destroyed.
Destroying variables refers to deallocating the memory that was allotted to the variables when
declaring it. We have written a few classes till now. You might have observed that not all
variables are the same. The ones declared in the body of a method were different from those
that were declared in the class itself. There are three types of variables: instance variables,
formal parameters or local variables and local variables.
Instance variables
Instance variables are those that are defined within a class itself and not in any method or
constructor of the class. They are known as instance variables because every instance of the
class (object) contains a copy of these variables. The scope of instance variables is determined
by the access specifier that is applied to these variables. We have already seen about it earlier.
The lifetime of these variables is the same as the lifetime of the object to which it belongs.
Object once created do not exist for ever. They are destroyed by the garbage collector of Java
when there are no more reference to that object. We shall see about Java's automatic garbage
collector later on.
Argument variables
These are the variables that are defined in the header oaf constructor or a method. The scope
of these variables is the method or constructor in which they are defined. The lifetime is
limited to the time for which the method keeps executing. Once the method finishes
execution, these variables are destroyed.
Local variables
A local variable is the one that is declared within a method or a constructor (not in the
header). The scope and lifetime are limited to the method itself.
One important distinction between these three types of variables is that access specifiers can
be applied to instance variables only and not to argument or local variables.
In addition to the local variables defined in a method, we also have variables that are defined
in bocks life an if block and an else block. The scope and is the same as that of the block
itself.

Operators in java
Operator in java is a symbol that is used to perform operations. For example: +, -, *, / etc.
There are many types of operators in java which are given below:
o Unary Operator,
o Arithmetic Operator,
o shift Operator,
o Relational Operator,
o Bitwise Operator,
o Logical Operator,
o Ternary Operator and
o Assignment Operator.
Operators Hierarchy

EXPRESSIONS
Expressions are essential building blocks of any Java program, usually created to produce a
new value, although sometimes an expression simply assigns a value to a variable. Expressions
are built using values, variables, operators and method calls.
Types of Expressions
While an expression frequently produces a result, it doesn't always. There are three types of
expressions in Java:
 Those that produce a value, i.e. the result of (1 + 1)

 Those that assign a variable, for example (v = 10)
 Those that have no result but might have a "side effect" because an expression can include
a wide range of elements such as method invocations or increment operators that modify
the state (i.e. memory) of a program.
Java Type casting and Type conversion
Widening or Automatic Type Conversion

Widening conversion takes place when two data types are automatically converted. This happens
when:
 The two data types are compatible.
 When we assign value of a smaller data type to a bigger data type.
For Example, in java the numeric data types are compatible with each other but no automatic
conversion is supported from numeric type to char or boolean. Also, char and boolean are not
compatible with each other.
Narrowing or Explicit Conversion

If we want to assign a value of larger data type to a smaller data type we perform explicit type
casting or narrowing.
 This is useful for incompatible data types where automatic conversion cannot be done.
 Here, target-type specifies the desired type to convert the specified value to.

Java Enum
Enum in java is a data type that contains fixed set of constants.
It can be used for days of the week (SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
THURSDAY, FRIDAY and SATURDAY) , directions (NORTH, SOUTH, EAST and WEST)
etc. The java enum constants are static and final implicitly. It is available from JDK 1.5.
Java Enums can be thought of as classes that have fixed set of constants.
Simple example of java enum

class EnumExample1{
public enum Season { WINTER, SPRING, SUMMER, FALL }

for (Season s : Season.values())
System.out.println(s);
}}
Output:
WINTER
SPRING
SUMMER
FALL
Control Flow Statements
The control flow statements in Java allow you to run or skip blocks of code when
special conditions are met.
The “if” Statement

The “if” statement in Java works exactly like in most programming languages. With the help of
“if” you can choose to execute a specific block of code when a predefined condition is met.
The structure of the “if” statement in Java looks like this:
if (condition) {
/ execute this code
}

The condition is Boolean. Boolean means it may be true or false. For example you may put
a mathematical equation as condition. Look at this full example:
Creating a Stand-Alone Java Application

1. Write a main method that runs your program. You can write this method anywhere. In
this example, I'll write my main method in a class called Main that has no other methods. For
example:
2. public class Main
3. {
4. public static void main(String[] args)
5. {
6. Game.play();
7. } }
8. Make sure your code is compiled, and that you have tested it thoroughly.
9. If you're using Windows, you will need to set your path to include Java, if you haven't
done so already. This is a delicate operation. Open Explorer, and look inside
C:\ProgramFiles\Java, and you should see some version of the JDK. Open this folder, and
then open the bin folder. Select the complete path from the top of the Explorer window,
and press Ctrl-C to copy it.
Next, find the "My Computer" icon (on your Start menu or desktop), right-click it, and
select properties. Click on the Advanced tab, and then click on the Environment variables
button. Look at the variables listed for all users, and click on the Path variable. Do not delete
the contents of this variable! Instead, edit the contents by moving the cursor to the right end,
entering a semicolon (;), and pressing Ctrl-V to paste the path you copied earlier. Then go
ahead and save your changes. (If you have any Cmd windows open, you will need to close
them.)
10. If you're using Windows, go to the Start menu and type "cmd" to run a program
that brings up a command prompt window. If you're using a Mac or Linux machine,
run the Terminal program to bring up a command prompt.
11. In Windows, type dir at the command prompt to list the contents of the current directory.
On a Mac or Linux machine, type ls to do this.

12. Now we want to change to the directory/folder that contains your compiled code. Look at
the listing of sub-directories within this directory, and identify which one contains your
code. Type cd followed by the name of that directory, to change to that directory. For
example, to change to a directory called Desktop, you would type:
cd Desktop
To change to the parent directory, type:
cd ..
Every time you change to a new directory, list the contents of that directory to see where to go
next. Continue listing and changing directories until you reach the directory that contains your
.class files.
13. If you compiled your program using Java 1.6, but plan to run it on a Mac, you'll need
to recompile your code from the command line, by typing:
javac -target 1.5 *.java
14. Now we'll create a single JAR file containing all of the files needed to run your program.
Arrays
Java provides a data structure, the array, which stores a fixed-size sequential collection of
elements of the same type. An array is used to store a collection of data, but it is often more
useful to think of an array as a collection of variables of the same type.
Instead of declaring individual variables, such as number0, number1, ..., and number99, you
declare one array variable such as numbers and use numbers[0], numbers[1], and ...,
numbers[99] to represent individual variables.
This tutorial introduces how to declare array variables, create arrays, and process arrays using
indexed variables.
Declaring Array Variables:

To use an array in a program, you must declare a variable to reference the array, and you must
specify the type of array the variable can reference. Here is the syntax for declaring an array
variable:
dataType[] arrayRefVar; // preferred way.

or
dataType arrayRefVar[]; // works but not preferred way.
Note: The style dataType[] arrayRefVar is preferred. The style dataType
arrayRefVar[] comes from the C/C++ language and was adopted in Java to accommodate C/C+
+ programmers.
Example:
The following code snippets are examples of this syntax:
double[] myList; // preferred way.

or
double myList[]; // works but not preferred way.
Creating Arrays:
You can create an array by using the new operator with the following syntax:
arrayRefVar = new dataType[arraySize];

The above statement does two things:
 It creates an array using new dataType[arraySize];
 It assigns the reference of the newly created array to the variable arrayRefVar.
Declaring an array variable, creating an array, and assigning the reference of the array to the
variable can be combined in one statement, as shown below:
dataType[] arrayRefVar = new dataType[arraySize];

Alternatively you can create arrays as follows:
dataType[] arrayRefVar = {value0, value1, ..., valuek};

The array elements are accessed through the index. Array indices are 0-based; that is, they start
from 0 to arrayRefVar.length-1.
Example:
Following statement declares an array variable, myList, creates an array of 10 elements of double
type and assigns its reference to myList:
double[] myList = new double[10];

Following picture represents array myList. Here, myList holds ten double values and the indices
are from 0 to 9.

Processing Arrays:
When processing array elements, we often use either for loop or for each loop because all of the
elements in an array are of the same type and the size of the array is known.
Example:
Here is a complete example of showing how to create, initialize and process arrays:
public class TestArray

{
double[] myList = {1.9, 2.9, 3.4, 3.5};
/ Print all the array elements for
(int i = 0; i < myList.length; i++) {
System.out.println(myList[i] + " ");
}
/ Summing all elements
double total = 0;
for (int i = 0; i < myList.length; i++) {
total += myList[i];
}
System.out.println("Total is " + total);
/ Finding the largest element
double max = myList[0];
for (int i = 1; i < myList.length; i++) { if
(myList[i] > max) max = myList[i];
}
System.out.println("Max is " + max);
}
}

This would produce the following result:
1.9
2.9
3.4
3.5
Total is 11.7
Max is 3.5
public class TestArray {
double[] myList = {1.9, 2.9, 3.4, 3.5};
// Print all the array elements
for (double element: myList) {
System.out.println(element);
}}}
Java Console Class
The Java Console class is be used to get input from console. It provides methods to read texts and
passwords.
If you read password using Console class, it will not be displayed to the user.
The java.io.Console class is attached with system console internally. The Console class is
introduced since 1.5.
Let's see a simple example to read text from console.
1. String text=System.console().readLine();
2. System.out.println("Text is: "+text);
Java Console Example
import java.io.Console;
class ReadStringTest{
public static void main(String args[]){
Console c=System.console();
System.out.println("Enter your name: ");
String n=c.readLine();
System.out.println("Welcome "+n); } }
Output
Enter your name: Nakul Jain

Welcome Nakul Jain
Constructors
Constructor in java is a special type of method that is used to initialize the object.
Java constructor is invoked at the time of object creation. It constructs the values i.e. provides
data for the object that is why it is known as constructor.
There are basically two rules defined for the constructor.
1. Constructor name must be same as its class name

2. Constructor must have no explicit return type
Types of java constructors
There are two types of constructors:
1. Default constructor (no-arg constructor)

2. Parameterized constructor
JAVA DEFAULT CONSTRUCTOR
A constructor that have no parameter is known as default constructor .
Syntax of default constructor:

1. <class_name>(){}
Example of default constructor
In this example, we are creating the no-arg constructor in the Bike class. It will be invoked at
the time of object creation.
class Bike1{
Bike1(){System.out.println("Bike is created");}
Bike1 b=new Bike1();
} }
Output: Bike is created

Example of parameterized constructor
In this example, we have created the constructor of Student class that have two parameters. We
can have any number of parameters in the constructor.
class Student4{
int id;
String name;
Student4(int i,String n){

id = i;
name = n;
}
void display(){System.out.println(id+" "+name);}

Student4 s1 = new Student4(111,"Sriyansh");
Student4 s2 = new Student4(222,"Devansh");
s1.display();
s2.display();
} }
Output:
111 Sriyansh
222 Devansh
Constructor Overloading in Java
Constructor overloading is a technique in Java in which a class can have any number of
constructors that differ in parameter lists.The compiler differentiates these constructors by
taking into account the number of parameters in the list and their type.
Example of Constructor Overloading

class Student5{
int id;
String name;
int age;
id = i;
name = n;
}
Student5(int i,String n,int a){
id = i;
name = n;
age=a;
}
void display(){System.out.println(id+" "+name+" "+age);}

Student5 s2 = new Student5(222,"Devansh",25);
s1.display();
s2.display();
} }
Output:
111 Sriyansh 0
222 Devansh 25
Java Copy Constructor
There is no copy constructor in java. But, we can copy the values of one object to another like
copy constructor in C++.
There are many ways to copy the values of one object into another in java. They are:
oBy constructor
oBy assigning the values of one object into another
oBy clone() method of Object class
In this example, we are going to copy the values of one object into another using java
constructor.
class Student6{
int id;
String name;
id = i;
name = n;
}
Student6(Student6 s){
id = s.id;
name =s.name;
}
void display(){System.out.println(id+" "+name);}

Student6 s1 = new Student6(111,"Kiran");
Student6 s2 = new Student6(s1);
s1.display();
s2.display();
} }
Output:
111 Kiran
111 Kiran

Java - Methods
A Java method is a collection of statements that are grouped together to perform an operation.
When you call the System.out.println() method, for example, the system actually executes
several statements in order to display a message on the console.
Now you will learn how to create your own methods with or without return values, invoke a
method with or without parameters, and apply method abstraction in the program design.
Creating Method
Considering the following example to explain the syntax of a method −
Syntax
public static int methodName(int a, int b) {

// body
}
Here,
 public static − modifier
 int − return type
 methodName − name of the method
 a, b − formal parameters
 int a, int b − list of parameters
Method definition consists of a method header and a method body. The same is shown in the
following syntax −
Syntax
modifier returnType nameOfMethod (Parameter List) {

// method body
}
The syntax shown above includes −
 modifier − It defines the access type of the method and it is optional to use.
 returnType − Method may return a value.
 nameOfMethod − This is the method name. The method signature consists of the
method name and the parameter list.

 Parameter List − The list of parameters, it is the type, order, and number of
parameters of a method. These are optional, method may contain zero parameters.
 method body − The method body defines what the method does with the statements.
Call by Value and Call by Reference in Java
There is only call by value in java, not call by reference. If we call a method passing a value, it
is known as call by value. The changes being done in the called method, is not affected in the
calling method.
Example of call by value in java

In case of call by value original value is not changed. Let's take a simple example:
class Operation{
int data=50;
void change(int data){
data=data+100;//changes will be in the local variable only
}
Operation op=new Operation();
System.out.println("before change "+op.data);
op.change(500);
System.out.println("after change "+op.data);
}
}
Output:before change 50
after change 50
In Java, parameters are always passed by value. For example, following program prints
i = 10, j = 20.
/ Test.java
class Test {
// swap() doesn't swap i and j
public static void swap(Integer i, Integer j) {
Integer temp = new Integer(i);
i = j;
j = temp;
}
Integer i = new Integer(10);
Integer j = new Integer(20);
swap(i, j);
System.out.println("i = " + i + ", j = " + j);

}
}
Static Fields and Methods
The static keyword in java is used for memory management mainly. We can apply java static
keyword with variables, methods, blocks and nested class. The static keyword belongs to the class
than instance of the class.
The static can be:
1. variable (also known as class variable)

2. method (also known as class method)
3. block
4. nested class
Java static variable
If you declare any variable as static, it is known static variable.
o The static variable can be used to refer the common property of all objects (that is not unique for
each object) e.g. company name of employees,college name of students etc.
o The static variable gets memory only once in class area at the time of class loading.
Advantage of static variable
It makes your program memory efficient (i.e it saves memory).
Understanding problem without static variable

1. class Student{
2. int rollno;
3. String name;
4. String college="ITS";
5. }
Example of static variable

//Program of static variable
class Student8{
int rollno;
String name;
static String college ="ITS";
Student8(int r,String n){
rollno = r;
name = n;
}
void display (){System.out.println(rollno+" "+name+"
"+college);} public static void main(String args[]){ Student8 s1 =
new Student8(111,"Sriyansh");
Student8 s2 = new Student8(222,"Devansh");
s1.display();
s2.display();
} }
Output:111 Sriyansh ITS
222 Devansh ITS
Java static method
If you apply static keyword with any method, it is known as static method.
o A static method belongs to the class rather than object of a class.

o A static method can be invoked without the need for creating an instance of a class.
o static method can access static data member and can change the value of it.
Example of static method

//Program of changing the common property of all objects(static field).
class Student9{
int rollno;
String name;
static String college = "ITS";
static void change(){
college = "BBDIT";
}
Student9(int r, String n){
rollno = r;
name = n;
}
void display (){System.out.println(rollno+" "+name+"
"+college);} public static void main(String args[]){
Student9.change();
Student9 s1 = new Student9 (111,"Sriyansh");
Student9 s2 = new Student9 (222,"Devansh");
Student9 s3 = new Student9 (333,"Sonoo");
s1.display();
s2.display();
s3.display();
} }
Output:111 Sriyansh BBDIT
222 Devansh BBDIT
333 Sonoo BBDIT
Java static block
o Is used to initialize the static data member.

o It is executed before main method at the time of class loading.
Example of static block

class A2{
static{System.out.println("static block is
invoked");} public static void main(String args[]){
System.out.println("Hello main");
} }
Output: static block is invoked
Hello main
Access Control
Access Modifiers in java
There are two types of modifiers in java: access modifiers and non-access modifiers.
The access modifiers in java specifies accessibility (scope) of a data member, method, constructor
or class.
There are 4 types of java access modifiers:

1. private
2. default
3. protected
4. public
private access modifier

The private access modifier is accessible only within class.
Simple example of private access modifier

In this example, we have created two classes A and Simple. A class contains private data
member and private method. We are accessing these private members from outside the class,
so there is compile time error.
class A{
private int data=40;
private void msg(){System.out.println("Hello java");} }
public class Simple{
A obj=new A();
System.out.println(obj.data);//Compile Time Error
obj.msg();//Compile Time Error
} }
2) default access modifier

If you don't use any modifier, it is treated as default bydefault. The default modifier is
accessible only within package.
Example of default access modifier

In this example, we have created two packages pack and mypack. We are accessing the A
class from outside its package, since A class is not public, so it cannot be accessed from outside
the package.
//save by A.java
package pack;
class A{
void msg(){System.out.println("Hello");}
}
//save by B.java
package mypack;
import pack.*;

class B{
A obj = new A();//Compile Time Error
obj.msg();//Compile Time Error } }
In the above example, the scope of class A and its method msg() is default so it cannot be
accessed from outside the package.
3) protected access modifier
The protected access modifier is accessible within package and outside the package but through
inheritance only.
The protected access modifier can be applied on the data member, method and constructor. It
can't be applied on the class.
Example of protected access modifier
In this example, we have created the two packages pack and mypack. The A class of pack
package is public, so can be accessed from outside the package. But msg method of this package
is declared as protected, so it can be accessed from outside the class only through inheritance.
//save by A.java
package pack;
public class A{
protected void msg(){System.out.println("Hello");} }
//save by B.java
package mypack;
import pack.*;
class B extends A{
B obj = new B();
obj.msg();
} }
Output:Hello
4) public access modifier

The public access modifier is accessible everywhere. It has the widest scope among all other
modifiers.
Example of public access modifier
//save by A.java
package pack;
public class A{
public void msg(){System.out.println("Hello");} }
//save by B.java
package mypack;
import pack.*;
class B{
A obj = new A();
obj.msg();
} }
Output:Hello
Understanding all java access modifiers
Let's understand the access modifiers by a simple table.
Access within within outside package by outside

Modifier Class package subclass only package
Private Y N N N
Default Y Y N N
Protected Y Y Y N
Public Y Y Y Y
this keyword in java
Usage of java this keyword
Here is given the 6 usage of java this keyword.
1. this can be used to refer current class instance variable.

2. this can be used to invoke current class method (implicitly)
3. this() can be used to invoke current class constructor.
4. this can be passed as an argument in the method call.
5. this can be passed as argument in the constructor call.
6. this can be used to return the current class instance from the method.
class Student{
int rollno;
String name;
float fee;
Student(int rollno,String name,float fee)
{ this.rollno=rollno;
this.name=name;
this.fee=fee;
}
void display(){System.out.println(rollno+" "+name+" "+fee);}
}
class TestThis2{
Student s1=new Student(111,"ankit",5000f);
Student s2=new
Student(112,"sumit",6000f); s1.display();
s2.display();
}}
Output:
111 ankit 5000
112 sumit 6000
Difference between constructor and method in java
Java Constructor Java Method
Constructor is used to initialize the state of an object. Method is used to expose behaviour
of an object.
Constructor must not have return type. Method must have return type.
Constructor is invoked implicitly. Method is invoked explicitly.
The java compiler provides a default constructor if you Method is not provided by compiler in
don't have any constructor. any case.
Constructor name must be same as the class name. Method name may or may not be

same as class name.
There are many differences between constructors and methods. They are given belo
Constructor Overloading in Java
Constructor overloading is a technique in Java in which a class can have any number of
constructors that differ in parameter lists.The compiler differentiates these constructors by
taking into account the number of parameters in the list and their type.
Example of Constructor Overloading

class Student5{
int id;
String name;
int age;
id = i;
name = n;
}
Student5(int i,String n,int a){
id = i;
name = n;
age=a;
}
void display(){System.out.println(id+" "+name+" "+age);}

Student5 s2 = new Student5(222,"Devansh",25);
s1.display();
s2.display();
}
}
Output:

111 Sriyansh 0
222 Devansh 25
Method Overloading in java
If a class has multiple methods having same name but different in parameters, it is known as
Method Overloading.
If we have to perform only one operation, having same name of the methods increases the
readability of the program.
Method Overloading: changing no. of arguments
In this example, we have created two methods, first add() method performs addition of two
numbers and second add method performs addition of three numbers.
In this example, we are creating static methods so that we don't need to create instance for calling
methods.
class Adder{
static int add(int a,int b){return a+b;}
static int add(int a,int b,int c){return a+b+c;}
}
class TestOverloading1{
public static void main(String[] args){
System.out.println(Adder.add(11,11));
System.out.println(Adder.add(11,11,11));
}}
Output:
22
33
Method Overloading: changing data type of arguments
In this example, we have created two methods that differs in data type. The first add method
receives two integer arguments and second add method receives two double arguments.

Recursion in Java
Recursion in java is a process in which a method calls itself continuously. A method in java
that calls itself is called recursive method.
Java Recursion Example 1: Factorial Number
public class RecursionExample3 {

static int factorial(int n){
if (n == 1)
return 1;
else
return(n * factorial(n-1));
} }
System.out.println("Factorial of 5 is: "+factorial(5));
}}
Output:
Factorial of 5 is: 120
Java Garbage Collection
In java, garbage means unreferenced objects.
Garbage Collection is process of reclaiming the runtime unused memory automatically. In other
words, it is a way to destroy the unused objects.
To do so, we were using free() function in C language and delete() in C++. But, in java it is
performed automatically. So, java provides better memory management.
Advantage of Garbage Collection
o It makes java memory efficient because garbage collector removes the unreferenced
objects from heap memory.
o It is automatically done by the garbage collector(a part of JVM) so we don't need to make
extra efforts.
gc() method
The gc() method is used to invoke the garbage collector to perform cleanup processing.
The gc() is found in System and Runtime classes.
public static void gc(){}
Simple Example of garbage collection in java

public class TestGarbage1{
public void finalize(){System.out.println("object is garbage collected");}
TestGarbage1 s1=new TestGarbage1();
TestGarbage1 s2=new TestGarbage1();
s1=null;
s2=null;
System.gc();
} }
object is garbage collected
object is garbage collected
Java String
string is basically an object that represents sequence of char values. An array of characters works
same as java string. For example:
1. char[] ch={'j','a','v','a','t','p','o','i','n','t'};
2. String s=new String(ch);
ssame as:
1. String s="javatpoint";
2. Java String class provides a lot of methods to perform operations on string such as
compare(), concat(), equals(), split(), length(), replace(), compareTo(), intern(), substring()
etc.
3. The java.lang.String class implements Serializable, Comparable and CharSequence
interfaces.
CharSequence Interface

The CharSequence interface is used to represent sequence of characters. It is implemented by
String, StringBuffer and StringBuilder classes. It means, we can create string in java by using
these 3 classes.
The java String is immutable i.e. it cannot be changed. Whenever we change any
string, a new instance is created. For mutable string, you can use StringBuffer and
StringBuilder classes.
There are two ways to create String object:
1. By string literal
2. By new keyword
String Literal
Java String literal is created by using double quotes. For Example:
1. String s="welcome";
Each time you create a string literal, the JVM checks the string constant pool first. If the string
already exists in the pool, a reference to the pooled instance is returned. If string doesn't exist in
the pool, a new string instance is created and placed in the pool. For example:
1. String s1="Welcome";
2. String s2="Welcome";//will not create new instance
By new keyword
1. String s=new String("Welcome");//creates two objects and one reference variable
In such case, JVM will create a new string object in normal (non pool) heap memory and the
literal "Welcome" will be placed in the string constant pool. The variable s will refer to the object
in heap (non pool).
Java String Example

public class StringExample{
String s1="java";//creating string by java string literal
char ch[]={'s','t','r','i','n','g','s'};
String s2=new String(ch);//converting char array to string
String s3=new String("example");//creating java string by new keyword
System.out.println(s1);
}}
java
strings
example
Immutable String in Java
In java, string objects are immutable. Immutable simply means unmodifiable or unchangeable.
Once string object is created its data or state can't be changed but a new string object is created.
Let's try to understand the immutability concept by the example given below:
class Testimmutablestring{
String s="Sachin";
s.concat(" Tendulkar");//concat() method appends the string at the end
System.out.println(s);//will print Sachin because strings are immutable objects
} }
Output:Sachin
class Testimmutablestring1{
String s="Sachin";
s=s.concat(" Tendulkar");
System.out.println(s);
} } Output:Sachin Tendulkar

Inheritance in Java
Inheritance in java is a mechanism in which one object acquires all the properties and
behaviors of parent object. Inheritance represents the IS-A relationship, also known as parent-
child relationship.
Why use inheritance in java

o For Method Overriding (so runtime polymorphism can be achieved).
o For Code Reusability.
Syntax of Java Inheritance

1. class Subclass-name extends Superclass-name
2. {
3. //methods and fields
4. }
The extends keyword indicates that you are making a new class that derives from an existing
class. The meaning of "extends" is to increase the functionality.
class Employee{
float salary=40000;
}
class Programmer extends Employee{
int bonus=10000;
public static void main(String args[]){ Programmer
p=new Programmer(); System.out.println("Programmer
salary is:"+p.salary); System.out.println("Bonus of
Programmer is:"+p.bonus);
} }
Programmer salary is:40000.0

Bonus of programmer is:10000
Types of inheritance in java
Single Inheritance Example
File: TestInheritance.java
class Animal{
void eat(){System.out.println("eating...");}
}
class Dog extends Animal{
void bark(){System.out.println("barking...");}
}
class TestInheritance{
Dog d=new Dog();
d.bark();
d.eat();
}}
Output:
barking...
eating...
Multilevel Inheritance Example
File: TestInheritance2.java
class Animal{
}
}
class BabyDog extends Dog{
void weep(){System.out.println("weeping...");}
}
class TestInheritance2{

BabyDog d=new BabyDog();
d.weep();
d.bark();
d.eat();
}}
Output:
weeping...
barking...
eating...
Hierarchical Inheritance Example
File: TestInheritance3.java
class Animal{
}
}
class Cat extends Animal{
void meow(){System.out.println("meowing...");}
}
class TestInheritance3{
Cat c=new Cat();
c.meow();
c.eat();
//c.bark();//C.T.Error
}}
Output:
meowing...
eating...

Member access and Inheritance
A subclass includes all of the members of its super class but it cannot access those members of
the super class that have been declared as private. Attempt to access a private variable would
cause compilation error as it causes access violation. The variables declared as private, is only
accessible by other members of its own class. Subclass have no access to it.
super keyword in java
The super keyword in java is a reference variable which is used to refer immediate parent class
object.
Whenever you create the instance of subclass, an instance of parent class is created implicitly
which is referred by super reference variable.
Usage of java super Keyword
1. super can be used to refer immediate parent class instance variable.
2. super can be used to invoke immediate parent class method.
3. super() can be used to invoke immediate parent class constructor.
super is used to refer immediate parent class instance variable.
class Animal{
String color="white";
}
String color="black";
void printColor(){
System.out.println(color);//prints color of Dog class
System.out.println(super.color);//prints color of Animal class
}
}
class TestSuper1{
Dog d=new Dog();

d.printColor();
}}
Output:
black
white
Final Keyword in Java
The final keyword in java is used to restrict the user. The java final keyword can be used in many context.
Final can be:
1. variable
2. method
3. class
The final keyword can be applied with the variables, a final variable that have no value it is called blank
final variable or uninitialized final variable. It can be initialized in the constructor only. The blank final
variable can be static also which will be initialized in the static block only.
Object class in Java
The Object class is the parent class of all the classes in java by default. In other words, it is the
topmost class of java.
The Object class is beneficial if you want to refer any object whose type you don't know. Notice
that parent class reference variable can refer the child class object, know as upcasting.
Let's take an example, there is getObject() method that returns an object but it can be of any type
like Employee,Student etc, we can use Object class reference to refer that object. For example:
1. Object obj=getObject();//we don't know what object will be returned from this method
The Object class provides some common behaviors to all the objects such as object can be
compared, object can be cloned, object can be notified etc.
Method Overriding in Java
If subclass (child class) has the same method as declared in the parent class, it is known
as method overriding in java.

Usage of Java Method Overriding
o Method overriding is used to provide specific implementation of a method that is already
provided by its super class.
o Method overriding is used for runtime polymorphism
Rules for Java Method Overriding

1. method must have same name as in the parent class
2. method must have same parameter as in the parent class.
3. must be IS-A relationship (inheritance).
Example of method overriding

Class Vehicle{
void run(){System.out.println("Vehicle is running");}
}
class Bike2 extends Vehicle{
void run(){System.out.println("Bike is running safely");}
public static void main(String args[]){ Bike2 obj = new
Bike2();
obj.run();
}
Output:Bike is running safely
1. class Bank{
int getRateOfInterest(){return 0;}
}
class SBI extends Bank{
}
class ICICI extends Bank{
}
class AXIS extends Bank{
}
class Test2{
SBI s=new SBI();
ICICI i=new ICICI();
AXIS a=new AXIS();
System.out.println("SBI Rate of Interest: "+s.getRateOfInterest());
System.out.println("ICICI Rate of Interest: "+i.getRateOfInterest());
System.out.println("AXIS Rate of Interest:
"+a.getRateOfInterest()); } }
Output:
SBI Rate of Interest: 8
ICICI Rate of Interest: 7
AXIS Rate of Interest: 9
Abstract class in Java
A class that is declared with abstract keyword is known as abstract class in java. It can have
abstract and non-abstract methods (method with body). It needs to be extended and its method
implemented. It cannot be instantiated.
Example abstract class

1. abstract class A{}
abstract method
1. abstract void printStatus();//no body and abstract
Example of abstract class that has abstract method

abstract class Bike{
abstract void run();
}
class Honda4 extends Bike{
void run(){System.out.println("running safely..");}
Bike obj = new Honda4();
obj.run();
}
1. }
running safely..
Interface in Java
An interface in java is a blueprint of a class. It has static constants and abstract methods.
The interface in java is a mechanism to achieve abstraction. There can be only abstract methods
in the java interface not method body. It is used to achieve abstraction and multiple inheritance in
Java.
Java Interface also represents IS-A relationship.
It cannot be instantiated just like abstract class.
There are mainly three reasons to use interface. They are given below.
o It is used to achieve abstraction.
o By interface, we can support the functionality of multiple inheritance.
o It can be used to achieve loose coupling.
Internal addition by compiler
Understanding relationship between classes and interfaces
//Interface declaration: by first user

interface Drawable{
void draw();
}
//Implementation: by second user
class Rectangle implements Drawable{
public void draw(){System.out.println("drawing rectangle");}
}
class Circle implements Drawable{
public void draw(){System.out.println("drawing
circle");} }
//Using interface: by third user
class TestInterface1{
Drawable d=new Circle();//In real scenario, object is provided by method e.g. getDrawable()
d.draw();
}}
Output:drawing circle
Multiple inheritance in Java by interface
interface Printable{

void print();
}
interface Showable{
void show();
}
class A7 implements Printable,Showable{ public
void print(){System.out.println("Hello");} public
void show(){System.out.println("Welcome");} public
static void main(String args[]){ A7 obj = new A7();
obj.print();
obj.show();
} }
Output:Hello
Welcome
Abstract class Interface
1) Abstract class can have abstract Interface can have only abstract methods. Since
and non-abstract methods. Java 8, it can have default and static
methods also.
2) Abstract class doesn't support Interface supports multiple inheritance.
multiple inheritance.
3) Abstract class can have final, non- Interface has only static and final variables.
final, static and non-static variables.
4) Abstract class can provide the Interface can't provide the implementation of
implementation of interface. abstract class.
5) The abstract keyword is used to The interface keyword is used to declare
declare abstract class. interface.
6) Example: Example:
public abstract class Shape{ public interface Drawable{
public abstract void draw(); void draw();
} }
Java Inner Classes

Java inner class or nested class is a class which is declared inside the class or interface.
We use inner classes to logically group classes and interfaces in one place so that it can be more
readable and maintainable.
Syntax of Inner class

1. class Java_Outer_class{
2. //code
3. class Java_Inner_class{
4. //code
5. } }
Advantage of java inner classes
There are basically three advantages of inner classes in java. They are as follows:
1) Nested classes represent a special type of relationship that is it can access all the members
(data members and methods) of outer class including private.
2) Nested classes are used to develop more readable and maintainable code because it
logically group classes and interfaces in one place only.
3) Code Optimization: It requires less code to write.
Difference between nested class and inner class in Java
Inner class is a part of nested class. Non-static nested classes are known as inner classes.
Types of Nested classes
There are two types of nested classes non-static and static nested classes.The non-static nested
classes are also known as inner classes.
o Non-static nested class (inner class)

1. Member inner class
2. Anonymous inner class
3. Local inner class
o Static nested class
Java Package
A java package is a group of similar types of classes, interfaces and sub-packages.
Package in java can be categorized in two form, built-in package and user-defined package.
There are many built-in packages such as java, lang, awt, javax, swing, net, io, util, sql etc.
Advantage of Java Package
1) Java package is used to categorize the classes and interfaces so that they can be easily
maintained.
2) Java package provides access protection.
3) Java package removes naming collision.
package mypack;
System.out.println("Welcome to package");
} }

How to compile java package
If you are not using any IDE, you need to follow the syntax given below:
javac -d directory javafilename

How to run java package program
To Compile: javac -d . Simple.java

To Run: java mypack.Simple
Using fully qualified name
Example of package by import fully qualified name
//save by A.java
package pack;
public class A{
public void msg(){System.out.println("Hello");} }
//save by B.java
package mypack;
class B{
pack.A obj = new pack.A();//using fully qualified name
obj.msg();
}
}
Output:Hello

UNIT-2
Exception Handling
The exception handling in java is one of the powerful mechanism to handle the runtime errors
so that normal flow of the application can be maintained.
What is exception
In java, exception is an event that disrupts the normal flow of the program. It is an object which is
thrown at runtime.
Advantage of Exception Handling
The core advantage of exception handling is to maintain the normal flow of the application.
Exception normally disrupts the normal flow of the application that is why we use exception
handling.
Types of Exception
There are mainly two types of exceptions: checked and unchecked where error is considered as
unchecked exception. The sun microsystem says there are three types of exceptions:
1. Checked Exception
2. Unchecked Exception
3. Error
Difference between checked and unchecked exceptions
1) Checked Exception: The classes that extend Throwable class except RuntimeException and Error are
known as checked exceptions e.g.IOException, SQLException etc. Checked exceptions are checked at
compile-time.
2) Unchecked Exception: The classes that extend RuntimeException are known as unchecked
exceptions e.g. ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException etc.
Unchecked exceptions are not checked at compile-time rather they are checked at runtime.
3) Error: Error is irrecoverable e.g. OutOfMemoryError, VirtualMachineError, AssertionError etc.

Hierarchy of Java Exception classes
Checked and UnChecked Exceptions

Java try block
Java try block is used to enclose the code that might throw an exception. It must be used within
the method.
Java try block must be followed by either catch or finally block.
Syntax of java try-catch
1. try{
2. //code that may throw exception
3. }catch(Exception_class_Name ref){}
Syntax of try-finally block
1. try{
2. //code that may throw exception
3. }finally{}
Java catch block
Java catch block is used to handle the Exception. It must be used after the try block only.
You can use multiple catch block with a single try.
Problem without exception handling
Let's try to understand the problem if we don't use try-catch block.
public class Testtrycatch1{

int data=50/0;//may throw exception
System.out.println("rest of the code...");
} }
Output:
Exception in thread main java.lang.ArithmeticException:/ by zero
As displayed in the above example, rest of the code is not executed (in such case, rest of
the code... statement is not printed).
There can be 100 lines of code after exception. So all the code after exception will not be
executed.
Solution by exception handling
Let's see the solution of above problem by java try-catch block.
public class Testtrycatch2{

try{
int data=50/0;
}catch(ArithmeticException e){System.out.println(e);}
} }
1. Output:
Exception in thread main java.lang.ArithmeticException:/ by
zero rest of the code...
Now, as displayed in the above example, rest of the code is executed i.e. rest of the code...
statement is printed.
Java Multi catch block
If you have to perform different tasks at the occurrence of different Exceptions, use java multi
catch block.
Let's see a simple example of java multi-catch block.
1. public class TestMultipleCatchBlock{

2. public static void main(String args[]){
3. try{
4. int a[]=new int[5];
5. a[5]=30/0;
6. }
7. catch(ArithmeticException e){System.out.println("task1 is completed");}
8. catch(ArrayIndexOutOfBoundsException e){System.out.println("task 2 completed");
9. }
10. catch(Exception e){System.out.println("common task completed");
11. }
12. System.out.println("rest of the code...");
13. } }
Output:task1 completed
rest of the code...
Java nested try example
Let's see a simple example of java nested try block.
class Excep6{
try{
try{
System.out.println("going to divide");
int b =39/0;
}catch(ArithmeticException e){System.out.println(e);}
try{

int a[]=new int[5];
a[5]=4;
}catch(ArrayIndexOutOfBoundsException e)
{System.out.println(e);} System.out.println("other statement);
}catch(Exception e){System.out.println("handeled");}
System.out.println("normal flow..");
}
1. }
Java finally block
Java finally block is a block that is used to execute important code such as closing connection,
stream etc.
Java finally block is always executed whether exception is handled or not.
Java finally block follows try or catch block.
Usage of Java finally
Case 1
Let's see the java finally example where exception doesn't occur.
class TestFinallyBlock{
try{
int data=25/5;
System.out.println(data);
}
catch(NullPointerException e){System.out.println(e);}
finally{System.out.println("finally block is always executed");}
System.out.println("rest of the code..."); }
}
Output:5
finally block is always executed
rest of the code...
Java throw keyword
The Java throw keyword is used to explicitly throw an exception.
We can throw either checked or uncheked exception in java by throw keyword. The throw
keyword is mainly used to throw custom exception. We will see custom exceptions later.
The syntax of java throw keyword is given below.
1. throw exception;

Java throw keyword example
In this example, we have created the validate method that takes integer value as a parameter.
If the age is less than 18, we are throwing the ArithmeticException otherwise print a message
welcome to vote.
1. public class TestThrow1{

static void validate(int age){
if(age<18)
throw new ArithmeticException("not valid");
else
System.out.println("welcome to vote");
}
validate(13);
} }
Output:
Exception in thread main java.lang.ArithmeticException:not valid

Java throws keyword
The Java throws keyword is used to declare an exception. It gives an information to the
programmer that there may occur an exception so it is better for the programmer to provide the
exception handling code so that normal flow can be maintained.
Exception Handling is mainly used to handle the checked exceptions. If there occurs any
unchecked exception such as NullPointerException, it is programmers fault that he is not
performing check up before the code being used.
Syntax of java throws

1. return_type method_name() throws exception_class_name{
2. //method code
3. }
4.
Java throws example
Let's see the example of java throws clause which describes that checked exceptions can be
propagated by throws keyword.
import java.io.IOException;
class Testthrows1{
void m()throws IOException{
throw new IOException("device error");//checked exception
}
void n()throws IOException{
m();
}
void p(){
try{
n();
}catch(Exception e){System.out.println("exception
handled");} }
Testthrows1 obj=new Testthrows1();
obj.p();
System.out.println("normal flow..."); } }
Output:
exception handled
normal flow...
Java Custom Exception
If you are creating your own Exception that is known as custom exception or user-defined
exception. Java custom exceptions are used to customize the exception according to user need.
By the help of custom exception, you can have your own exception and message.
Let's see a simple example of java custom exception.
class InvalidAgeException extends Exception{

InvalidAgeException(String s){
super(s);
}}
class TestCustomException1{
static void validate(int age)throws InvalidAgeException{
if(age<18)
throw new InvalidAgeException("not valid");
else
System.out.println("welcome to vote");
}
try{
validate(13);
}catch(Exception m){System.out.println("Exception occured: "+m);}

} }
Output:Exception occured: InvalidAgeException:not valid rest of the code...

Multithreading
Multithreading in java is a process of executing multiple threads simultaneously.
Thread is basically a lightweight sub-process, a smallest unit of processing. Multiprocessing and

multithreading, both are used to achieve multitasking.
But we use multithreading than multiprocessing because threads share a common memory area.
They don't allocate separate memory area so saves memory, and context-switching between the
threads takes less time than process.
Java Multithreading is mostly used in games, animation etc.
Advantages of Java Multithreading
1) It doesn't block the user because threads are independent and you can perform multiple
operations at same time.
2) You can perform many operations together so it saves time.
3) Threads are independent so it doesn't affect other threads if exception occur in a single thread.
Life cycle of a Thread (Thread States)
A thread can be in one of the five states. According to sun, there is only 4 states in thread life
cycle in java new, runnable, non-runnable and terminated. There is no running state.
But for better understanding the threads, we are explaining it in the 5 states.
The life cycle of the thread in java is controlled by JVM. The java thread states are as follows:
1. New
2. Runnable
3. Running
4. Non-Runnable (Blocked)
5. Terminated

How to create thread
There are two ways to create a thread:
1. By extending Thread class

2. By implementing Runnable interface.
Thread class:
Thread class provide constructors and methods to create and perform operations on a
thread.Thread class extends Object class and implements Runnable interface.
Commonly used Constructors of Thread class:
oThread()
oThread(String name)
oThread(Runnable r)
oThread(Runnable r,String name)

Commonly used methods of Thread class:
1. public void run(): is used to perform action for a thread.

2. public void start(): starts the execution of the thread.JVM calls the run() method on the thread.
3. public void sleep(long miliseconds): Causes the currently executing thread to sleep (temporarily
cease execution) for the specified number of milliseconds.
4. public void join(): waits for a thread to die.
5. public void join(long miliseconds): waits for a thread to die for the specified miliseconds.
6. public int getPriority(): returns the priority of the thread.
7. public int setPriority(int priority): changes the priority of the thread.
8. public String getName(): returns the name of the thread.
9. public void setName(String name): changes the name of the thread.
10. public Thread currentThread(): returns the reference of currently executing thread.
11. public int getId(): returns the id of the thread.
12. public Thread.State getState(): returns the state of the thread.
13. public boolean isAlive(): tests if the thread is alive.
14. public void yield(): causes the currently executing thread object to temporarily pause and allow
other threads to execute.
15. public void suspend(): is used to suspend the thread(depricated).
16. public void resume(): is used to resume the suspended thread(depricated).
17. public void stop(): is used to stop the thread(depricated).
18. public boolean isDaemon(): tests if the thread is a daemon thread.
19. public void setDaemon(boolean b): marks the thread as daemon or user thread.
20. public void interrupt(): interrupts the thread.
21. public boolean isInterrupted(): tests if the thread has been interrupted.
22. public static boolean interrupted(): tests if the current thread has been interrupted.
Runnable interface:
The Runnable interface should be implemented by any class whose instances are intended to
be executed by a thread. Runnable interface have only one method named run().
1. public void run(): is used to perform action for a thread.
Starting a thread:
start() method of Thread class is used to start a newly created thread. It performs
following tasks:
oA new thread starts(with new callstack).
oThe thread moves from New state to the Runnable state.
oWhen the thread gets a chance to execute, its target run() method will run.

Java Thread Example by extending Thread class
class Multi extends Thread{

public void run(){
System.out.println("thread is running...");
}
Multi t1=new Multi();
t1.start();
}}
Output:thread is running...
Java Thread Example by implementing Runnable interface
class Multi3 implements Runnable{

public void run(){
System.out.println("thread is running...");
}
Multi3 m1=new Multi3();
Thread t1 =new Thread(m1);
t1.start();
} }
Output:thread is running...
Priority of a Thread (Thread Priority):

Each thread have a priority. Priorities are represented by a number between 1 and 10. In most
cases, thread schedular schedules the threads according to their priority (known as
preemptive scheduling). But it is not guaranteed because it depends on JVM specification
that which scheduling it chooses.
3 constants defined in Thread class:
1. public static int MIN_PRIORITY

2. public static int NORM_PRIORITY
3. public static int MAX_PRIORITY
Default priority of a thread is 5 (NORM_PRIORITY). The value of MIN_PRIORITY is 1

and the value of MAX_PRIORITY is 10.
Example of priority of a Thread:

class TestMultiPriority1 extends Thread{
public void run(){
System.out.println("running thread name is:"+Thread.currentThread().getName());
System.out.println("running thread priority is:"+Thread.currentThread().getPriority());
}

TestMultiPriority1 m1=new TestMultiPriority1();
TestMultiPriority1 m2=new TestMultiPriority1();
m1.setPriority(Thread.MIN_PRIORITY);
m2.setPriority(Thread.MAX_PRIORITY);
m1.start();
m2.start();
} }
Output:running thread name is:Thread-0
running thread priority is:10
running thread name is:Thread-1
running thread priority is:1
Java synchronized method
If you declare any method as synchronized, it is known as synchronized method.
Synchronized method is used to lock an object for any shared resource.
When a thread invokes a synchronized method, it automatically acquires the lock for that
object and releases it when the thread completes its task.
Example of inter thread communication in java
Let's see the simple example of inter thread communication.
class Customer{
int amount=10000;
synchronized void withdraw(int amount){
System.out.println("going to withdraw...");
if(this.amount<amount){
System.out.println("Less balance; waiting for
deposit..."); try{wait();}catch(Exception e){} }
this.amount-=amount;
System.out.println("withdraw completed...");
}
synchronized void deposit(int amount){
System.out.println("going to deposit...");
this.amount+=amount;
System.out.println("deposit completed... ");
notify();
}
}
class Test{
final Customer c=new Customer();
new Thread(){
public void run(){c.withdraw(15000);}
}.start();
new Thread(){
public void run(){c.deposit(10000);}
}
start();
}}
Output: going to withdraw...
Less balance; waiting for deposit...
going to deposit...
deposit completed...
withdraw completed
ThreadGroup in Java
Java provides a convenient way to group multiple threads in a single object. In such way, we can
suspend, resume or interrupt group of threads by a single method call.
Note: Now suspend(), resume() and stop() methods are deprecated.
Java thread group is implemented by java.lang.ThreadGroup class.
Constructors of ThreadGroup class
There are only two constructors of ThreadGroup class.
ThreadGroup(String name)
ThreadGroup(ThreadGroup parent, String name)
Let's see a code to group multiple threads.
1. ThreadGroup tg1 = new ThreadGroup("Group A");

2. Thread t1 = new Thread(tg1,new MyRunnable(),"one");
3. Thread t2 = new Thread(tg1,new MyRunnable(),"two");
4. Thread t3 = new Thread(tg1,new MyRunnable(),"three");
Now all 3 threads belong to one group. Here, tg1 is the thread group name, MyRunnable is the
class that implements Runnable interface and "one", "two" and "three" are the thread names.
Now we can interrupt all threads by a single line of code only.
1. Thread.currentThread().getThreadGroup().interrupt();
Exploring java.net and java.text

java.net
The term network programming refers to writing programs that execute across multiple devices
(computers), in which the devices are all connected to each other using a network.
The java.net package of the J2SE APIs contains a collection of classes and interfaces that
provide the low-level communication details, allowing you to write programs that focus on
solving the problem at hand.
The java.net package provides support for the two common network protocols −
 TCP − TCP stands for Transmission Control Protocol, which allows for reliable
communication between two applications. TCP is typically used over the Internet
Protocol, which is referred to as TCP/IP.
 UDP − UDP stands for User Datagram Protocol, a connection-less protocol that
allows for packets of data to be transmitted between applications.
This chapter gives a good understanding on the following two subjects −
 Socket Programming − This is the most widely used concept in Networking and it
has been explained in very detail.
 URL Processing − This would be covered separately.
java.text
The java.text package is necessary for every java developer to master because it has a lot of
classes that is helpful in formatting such as dates, numbers, and messages.
java.text Classes
The following are the classes available for java.text package
[table]
Class|Description
SimpleDateFormat|is a concrete class that helps in formatting and parsing of dates.
[/table]

UNIT-4
Collection Framework in Java
Collections in java is a framework that provides an architecture to store and manipulate the group
of objects.
All the operations that you perform on a data such as searching, sorting, insertion, manipulation,
deletion etc. can be performed by Java Collections.
Java Collection simply means a single unit of objects. Java Collection framework provides many
interfaces (Set, List, Queue, Deque etc.) and classes (ArrayList, Vector, LinkedList,
PriorityQueue, HashSet, LinkedHashSet, TreeSet etc).
What is framework in java

o provides readymade architecture.
o represents set of classes and interface.
o is optional.
What is Collection framework
Collection framework represents a unified architecture for storing and manipulating group of
objects. It has:
1. Interfaces and its implementations i.e. classes

2. Algorithm

Hierarchy of Collection Framework
Java ArrayList class

Java ArrayList class uses a dynamic array for storing the elements. It inherits AbstractList class
and implements List interface.
The important points about Java ArrayList class are:
o Java ArrayList class can contain duplicate elements.

o Java ArrayList class maintains insertion order.
o Java ArrayList class is non synchronized.
o Java ArrayList allows random access because array works at the index basis.
o In Java ArrayList class, manipulation is slow because a lot of shifting needs to be occurred
if any element is removed from the array list.

ArrayList class declaration
Let's see the declaration for java.util.ArrayList class.
Constructors of Java ArrayList
Constructor Description
ArrayList() It is used to build an empty array list.
ArrayList(Collection It is used to build an array list that is initialized with the

c) elements of the collection c.
ArrayList(int It is used to build an array list that has the specified

capacity) initial capacity.
Java ArrayList Example

import java.util.*;
class TestCollection1{
ArrayList<String> list=new ArrayList<String>();//Creating arraylist
list.add("Ravi");//Adding object in arraylist list.add("Vijay");
list.add("Ravi");
list.add("Ajay");
//Traversing list through Iterator
Iterator itr=list.iterator();
while(itr.hasNext()){
System.out.println(itr.next()); } }}
Ravi
Vijay
Ravi
Ajay

vector
ArrayList and Vector both implements List interface and maintains insertion order.
But there are many differences between ArrayList and Vector classes that are given below.
ArrayList Vector
1) ArrayList is not synchronized. Vector is synchronized.
2)ArrayList increments50% of Vector increments 100% means doubles the array

current array size if number of size if total number of element exceeds than its
element exceeds from its capacity. capacity.
3)ArrayList is not a legacy class, Vector is a legacy class.

it is introduced in JDK 1.2.
4) ArrayList is fast because it is Vector is slow because it is synchronized i.e. in

non-synchronized. multithreading environment, it will hold the other
threads in runnable or non-runnable state until
current thread releases the lock of object.
5) ArrayLis tuses Iterator interface Vector uses Enumeration interface to traverse the
to traverse the elements. elements. But it can use Iterator also.
Example of Java Vector
Let's see a simple example of java Vector class that uses Enumeration interface.
1. import java.util.*;
2. class TestVector1{
3. public static void main(String args[]){
4. Vector<String> v=new Vector<String>();//creating vector
5. v.add("umesh");//method of Collection
6. v.addElement("irfan");//method of Vector
7. v.addElement("kumar");
8. //traversing elements using Enumeration

9. Enumeration e=v.elements();
10. while(e.hasMoreElements()){
11. System.out.println(e.nextElement());
12. } } }
Output:
umesh
irfan
kumar
Java Hashtable class
Java Hashtable class implements a hashtable, which maps keys to values. It inherits Dictionary
class and implements the Map interface.
The important points about Java Hashtable class are:
o A Hashtable is an array of list. Each list is known as a bucket. The position of bucket is
identified by calling the hashcode() method. A Hashtable contains values based on the
key.
o It contains only unique elements.
o It may have not have any null key or value.
o It is synchronized.
Hashtable class declaration
Let's see the declaration for java.util.Hashtable class.
1. public class Hashtable<K,V> extends Dictionary<K,V> implements Map<K,V>, Cloneable, Ser

ializable
Hashtable class Parameters
Let's see the Parameters for java.util.Hashtable class.
o K: It is the type of keys maintained by this map.

o V: It is the type of mapped values.

Constructors of Java Hashtable class
Constructor Description
Hashtable() It is the default constructor of hash table it instantiates the

Hashtable class.
Hashtable(int size) It is used to accept an integer parameter and creates a hash table
that has an initial size specified by integer value size.
Hashtable(int size, float It is used to create a hash table that has an initial size specified by
fillRatio) size and a fill ratio specified by fillRatio.
Java Hashtable Example

import java.util.*;
class TestCollection16{
Hashtable<Integer,String> hm=new Hashtable<Integer,String>();
hm.put(100,"Amit");
hm.put(102,"Ravi");
hm.put(101,"Vijay");
hm.put(103,"Rahul");
for(Map.Entry m:hm.entrySet()){
System.out.println(m.getKey()+" "+m.getValue());
} } }
Output:
103 Rahul
102 Ravi
101 Vijay
100 Amit
Stack
Stack is a subclass of Vector that implements a standard last-in, first-out stack.
Stack only defines the default constructor, which creates an empty stack. Stack includes all the
methods defined by Vector, and adds several of its own.

Stack( )
Example
The following program illustrates several of the methods supported by this collection −
import java.util.*;
public class StackDemo {
static void showpush(Stack st, int a) {
st.push(new Integer(a));
System.out.println("push(" + a + ")");
System.out.println("stack: " + st);}
static void showpop(Stack st) {
System.out.print("pop -> ");
Integer a = (Integer) st.pop();
System.out.println(a);
System.out.println("stack: " + st); }
public static void main(String args[]) {
Stack st = new Stack();
System.out.println("stack: " + st);
showpush(st, 42);
showpush(st, 66);
showpush(st, 99);
showpop(st);
showpop(st);
showpop(st);
try {
showpop(st);
} catch (EmptyStackException e) {
System.out.println("empty stack");
}}}
This will produce the following result −
Output
stack: [ ]
push(42)
stack: [42]
push(66)
stack: [42, 66]
push(99)
stack: [42, 66, 99]
pop -> 99
stack: [42, 66]
pop -> 66
stack: [42]
pop -> 42
stack: [ ]
pop -> empty stack
Enumeration
The Enumeration Interface
The Enumeration interface defines the methods by which you can enumerate (obtain one at a
time) the elements in a collection of objects.
The methods declared by Enumeration are summarized in the following table −
Sr.No. Method & Description
1
boolean hasMoreElements( )
When implemented, it must return true while there are still more elements to extract, and
false when all the elements have been enumerated.
2
Object nextElement( )
This returns the next object in the enumeration as a generic Object reference.
Example

Following is an example showing usage of Enumeration.
import java.util.Vector;
import java.util.Enumeration;
public class EnumerationTester {
public static void main(String args[]) {
Enumeration days;
Vector dayNames = new Vector();
dayNames.add("Sunday");
dayNames.add("Monday");
dayNames.add("Tuesday");
dayNames.add("Wednesday");
dayNames.add("Thursday");
dayNames.add("Friday");
dayNames.add("Saturday");
days = dayNames.elements();
while (days.hasMoreElements()) {
System.out.println(days.nextElement());
} }}
This will produce the following result −
Output
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Iterator
It is a universal iterator as we can apply it to any Collection object. By using Iterator, we can
perform both read and remove operations. It is improved version of Enumeration with additional
functionality of remove-ability of a element.
Iterator must be used whenever we want to enumerate elements in all Collection framework
implemented interfaces like Set, List, Queue, Deque and also in all implemented classes of Map
interface. Iterator is the only cursor available for entire collection framework.
Iterator object can be created by calling iterator() method present in Collection interface.
/ Here "c" is any Collection object. itr is of
/ type Iterator interface and refers to "c"

Iterator itr = c.iterator();
Iterator interface defines three methods:
/ Returns true if the iteration has more elements
public boolean hasNext();
/ Returns the next element in the iteration

/ It throws NoSuchElementException if no more
/ element present
public Object next();
/ Remove the next element in the iteration

/ This method can be called only once per call
/ to next()
public void remove();

remove() method can throw two exceptions
 UnsupportedOperationException : If the remove operation is not supported by this iterator
 IllegalStateException : If the next method has not yet been called, or the remove method
has already been called after the last call to the next method
Limitations of Iterator:
 Only forward direction iterating is possible.
 Replacement and addition of new element is not supported by Iterator.
StringTokenizer in Java
The java.util.StringTokenizer class allows you to break a string into tokens. It is simple way to
break string.
It doesn't provide the facility to differentiate numbers, quoted strings, identifiers etc.
Constructors of StringTokenizer class
There are 3 constructors defined in the StringTokenizer class.

Constructor
Description
StringTokenizer(String str) creates StringTokenizer with specified string.
StringTokenizer(String str, creates StringTokenizer with specified string and

String delim) delimeter.
StringTokenizer(String str, creates StringTokenizer with specified string, delimeter

String delim, boolean and returnValue. If return value is true, delimiter
returnValue) characters are considered to be tokens. If it is false,
delimiter characters serve to separate tokens.
Methods of StringTokenizer class
The 6 useful methods of StringTokenizer class are as follows:
Public method Description
boolean hasMoreTokens() checks if there is more tokens available.
String nextToken() returns the next token from the StringTokenizer object.
String nextToken(String delim) returns the next token based on the delimeter.
boolean hasMoreElements() same as hasMoreTokens() method.
Object nextElement() same as nextToken() but its return type is Object.
int countTokens() returns the total number of tokens.
Simple example of StringTokenizer class
Let's see the simple example of StringTokenizer class that tokenizes a string "my name is khan"
on the basis of whitespace.
import java.util.StringTokenizer;

StringTokenizer st = new StringTokenizer("my name is khan"," ");
while (st.hasMoreTokens()) {
System.out.println(st.nextToken());
} } }
Output:my
name
is
khan
Example of nextToken(String delim) method of StringTokenizer class
import java.util.*;
public class Test {
StringTokenizer st = new StringTokenizer("my,name,is,khan");
// printing next token
System.out.println("Next token is : " + st.nextToken(","));
} }
Output:Next token is : my
java.util.Random
 For using this class to generate random numbers, we have to first create an instance of this
class and then invoke methods such as nextInt(), nextDouble(), nextLong() etc using that
instance.
 We can generate random numbers of types integers, float, double, long, booleans using this
class.
 We can pass arguments to the methods for placing an upper bound on the range of the
numbers to be generated. For example, nextInt(6) will generate numbers in the range 0 to 5
both inclusive.
/ A Java program to demonstrate random number generation
/ using java.util.Random;
import java.util.Random;
public class generateRandom{
public static void main(String args[])

{
/ create instance of Random class
Random rand = new Random();
/ Generate random integers in range 0 to 999

int rand_int1 = rand.nextInt(1000);
int rand_int2 = rand.nextInt(1000);

/ Print random integers System.out.println("Random
Integers: "+rand_int1); System.out.println("Random
Integers: "+rand_int2);
/ Generate Random doubles

double rand_dub1 = rand.nextDouble();
double rand_dub2 = rand.nextDouble();
// Print random doubles

System.out.println("Random Doubles: "+rand_dub1);
System.out.println("Random Doubles: "+rand_dub2);
}}
Output:
Random Integers: 547

Random Integers: 126
Random Doubles: 0.8369779739988428
Random Doubles: 0.5497554388209912
Java Scanner class
There are various ways to read input from the keyboard, the java.util.Scanner class is one of them.
The Java Scanner class breaks the input into tokens using a delimiter that is whitespace
bydefault. It provides many methods to read and parse various primitive values.
Java Scanner class is widely used to parse text for string and primitive types using regular
expression.
Java Scanner class extends Object class and implements Iterator and Closeable interfaces.
Commonly used methods of Scanner class
There is a list of commonly used Scanner class methods:
Method Description
public String next() it returns the next token from the scanner.
public String nextLine() it moves the scanner position to the next line and returns the value
as a string.
public byte nextByte() it scans the next token as a byte.

public short nextShort()
it scans the next token as a short value.
public int nextInt() it scans the next token as an int value.
public long nextLong() it scans the next token as a long value.
public float nextFloat() it scans the next token as a float value.
public double it scans the next token as a double value.

nextDouble()
Java Scanner Example to get input from console
Let's see the simple example of the Java Scanner class which reads the int, string and double
value as an input:
import java.util.Scanner;
class ScannerTest{
Scanner sc=new Scanner(System.in);
System.out.println("Enter your rollno");
int rollno=sc.nextInt();
System.out.println("Enter your name");
String name=sc.next();
System.out.println("Enter your fee");
double fee=sc.nextDouble();
System.out.println("Rollno:"+rollno+" name:"+name+" fee:"+fee);
sc.close();
} } Output:
Enter your rollno

111
Enter your name
Ratan
Enter
450000
Rollno:111 name:Ratan fee:450000

Java Calendar Class
Java Calendar class is an abstract class that provides methods for converting date between a
specific instant in time and a set of calendar fields such as MONTH, YEAR, HOUR, etc. It
inherits Object class and implements the Comparable interface.
Java Calendar class declaration
Let's see the declaration of java.util.Calendar class.
1. public abstract class Calendar extends Object

2. implements Serializable, Cloneable, Comparable<Calendar>
Java Calendar Class Example
import java.util.Calendar;
public class CalendarExample1 {
Calendar calendar = Calendar.getInstance();
System.out.println("The current date is : " + calendar.getTime());
calendar.add(Calendar.DATE, -15);
System.out.println("15 days ago: " + calendar.getTime());
calendar.add(Calendar.MONTH, 4);
System.out.println("4 months later: " + calendar.getTime());
calendar.add(Calendar.YEAR, 2);
System.out.println("2 years later: " + calendar.getTime());
} }
Output:
The current date is : Thu Jan 19 18:47:02 IST 2017

15 days ago: Wed Jan 04 18:47:02 IST 2017
4 months later: Thu May 04 18:47:02 IST 2017
2 years later: Sat May 04 18:47:02 IST 2019

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UNIT-1

Simula is considered as the first object-oriented programming language. The programming

Smalltalk is considered as the first truly object-oriented programming language.

OOPs (Object Oriented Programming System)

Collection of objects is called class. It is a logical entity.

In java, we use method overloading and method overriding to achieve polymorphism.

In java, we use abstract class and interface to achieve abstraction.

JAVA PROGRAMMING PAGE 2

JAVA PROGRAMMING PAGE 3

Currently, Java is used in internet programming, mobile devices, games, e-business

Java Version History

1. JDK Alpha and Beta (1995)

JAVA PROGRAMMING PAGE 4

Types of Java Comments

There are 3 types of comments in java.

1. Single Line Comment

Java Single Line Comment

The single line comment is used to comment only one line.

1. //This is single line comment

JAVA PROGRAMMING PAGE 5

public class CommentExample1 {

Java Multi Line Comment

The multi line comment is used to comment multiple lines of code.

public class CommentExample2 {

JAVA PROGRAMMING PAGE 6

Compile it by javac tool:

Create Documentation API by javadoc tool:

JAVA PROGRAMMING PAGE 7

o Primitive data types

Data Type Default Value Default size

boolean False 1 bit

char '\u0000' 2 byte

float 0.0f 4 byte

double 0.0d 8 byte

Java Variable Example: Add Two Numbers

JAVA PROGRAMMING PAGE 8

There are three types of variables in java:

A variable which is declared inside the method is called local variable.

A variable that is declared as static is called static variable. It cannot be local.

We will have detailed learning of these variables in next chapters.

Example to understand the types of variables in java

modifier static final dataType variableName = value; //constant within a c

JAVA PROGRAMMING PAGE 9

JAVA PROGRAMMING PAGE 10

JAVA PROGRAMMING PAGE 11

 Those that produce a value, i.e. the result of (1 + 1)

Java Type casting and Type conversion

Widening or Automatic Type Conversion

Narrowing or Explicit Conversion

JAVA PROGRAMMING PAGE 12

Enum in java is a data type that contains fixed set of constants.

Simple example of java enum

public static void main(String[] args) {

Control Flow Statements

The “if” Statement

JAVA PROGRAMMING PAGE 13

Creating a Stand-Alone Java Application

JAVA PROGRAMMING PAGE 14

To change to the parent directory, type: