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    Object-Oriented Programming (CS F213) Lecture - 2 (Introduction To Java)

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    VSD VISHNU
    This document discusses Java and how to create a basic Java application. It explains that Java source code is compiled into bytecode that can run on any Java Virtual Machine (JVM). The key aspects of a basic Java application are: 1. Every application needs a main method with the signature public static void main(String[] args) as the entry point. 2. The main method is used to invoke methods on objects to run the application logic. 3. A simple example application is provided that defines a Bicycle class with methods like changeGear() and prints its state. 4. To run the application, two Bicycle objects are created and methods like speedUp() are called on each to

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    Object-Oriented Programming (CS F213) Lecture - 2 (Introduction To Java)

    Uploaded by

    VSD VISHNU
    23 views14 pages
    This document discusses Java and how to create a basic Java application. It explains that Java source code is compiled into bytecode that can run on any Java Virtual Machine (JVM). The key aspects of a basic Java application are: 1. Every application needs a main method with the signature public static void main(String[] args) as the entry point. 2. The main method is used to invoke methods on objects to run the application logic. 3. A simple example application is provided that defines a Bicycle class with methods like changeGear() and prints its state. 4. To run the application, two Bicycle objects are created and methods like speedUp() are called on each to

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    This document discusses Java and how to create a basic Java application. It explains that Java source code is compiled into bytecode that can run on any Java Virtual Machine (JVM). The key aspects of a basic Java application are: 1. Every application needs a main method with the signature public static void main(String[] args) as the entry point. 2. The main method is used to invoke methods on objects to run the application logic. 3. A simple example application is provided that defines a Bicycle class with methods like changeGear() and prints its state. 4. To run the application, two Bicycle objects are created and methods like speedUp() are called on each to

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    23 views14 pages

    Object-Oriented Programming (CS F213) Lecture - 2 (Introduction To Java)

    Uploaded by

    VSD VISHNU
    This document discusses Java and how to create a basic Java application. It explains that Java source code is compiled into bytecode that can run on any Java Virtual Machine (JVM). The key aspects of a basic Java application are: 1. Every application needs a main method with the signature public static void main(String[] args) as the entry point. 2. The main method is used to invoke methods on objects to run the application logic. 3. A simple example application is provided that defines a Bicycle class with methods like changeGear() and prints its state. 4. To run the application, two Bicycle objects are created and methods like speedUp() are called on each to

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    BITS Pilani

    Pilani Campus

    Object-Oriented Programming (CS F213)

    Lecture -2 [Introduction to Java]


    JavaTM Technology

    • Characterized by the  Each of these keywords are


    following keywords very well explained in “Java
     Simple Language Environment”, a
     Architecture Neutral white paper written by James
     Objected Oriented

    Gosling and Henry McGilton
    Portable
     Distributed
     Multithreaded
     High Performance
     Robust
     Dynamic
     Secure

    2
    BITS Pilani, Pilani Campus
    The JavaTM Programming Language

    • All source code is first written in plain text files ending with the .java
    extension
    • Those source files are then compiled into .class files by the javac
    compiler
    • A .class file does not contain code that is native to your processor;
    it instead contains bytecodes — the machine language of the Java
    Virtual Machine (Java VM)
    • The java launcher tool then runs your application with an instance
    of the Java Virtual Machine
    3
    BITS Pilani, Pilani Campus
    The JavaTM Programming Language

    • Because the Java VM is


    available on many
    different operating
    systems, the
    same .class files are
    capable of running on
    Microsoft Windows, the
    Solaris TM Operating
    System (Solaris OS),
    Linux, or Mac OS

    • Through the Java VM,


    the same application is
    capable of running on
    multiple platforms.

    4
    BITS Pilani, Pilani Campus
    The Java Platform

    • A platform is the hardware


    or software environment in
    which a program runs
    • Microsoft Windows, Linux,
    Solaris OS, and Mac OS
    • Most platforms can be  The Java platform has two
    described as a components:
    combination of the ◦ The Java Virtual Machine
    operating system and ◦ The Java Application Programming
    underlying hardware Interface (API)
    • The Java platform differs  The API is a large collection of ready-
    from most other platforms made software components that
    in that it's a software-only provide many useful capabilities. It is
    platform that runs on top grouped into libraries of related classes
    of other hardware-based and interfaces; these libraries are
    platforms.
    known as packages 5
    BITS Pilani, Pilani Campus
    Creating Your First Application

    • Checklist
    – The Java SE Development Kit
    – A text editor

     Creating application using simple text


    editor
     Install JDK
     Check for correct installation
     Create HelloWorldApp.java
     Compile HelloWorldApp.java
     Run HelloWorldApp

     Creating application using Eclipse

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    BITS Pilani, Pilani Campus
    A Closer Look at HelloWorldApp

    The HelloWorldApp class implements an application that


    simply prints "Hello World!" to standard output.
    class HelloWorldApp {
    public static void main(String[] args) {
    The HelloWorldApp // Display the string.
    class definition System.out.println("Hello World!");
    }
    }
    The most basic
    form of a class  Every application in Java should have a
    definition is main() method
     modifiers public and static can be written in
    class name { either order
    ...  It is the entry point of your application
    }  Accepts a single argument which is an array
    of elements of type String
     Mechanism through which the runtime
    system passes information to your application

    7 BITS Pilani, Pilani Campus


    A Sample Java Program

    8
    BITS Pilani, Pilani Campus
    System.out.println

    • Java programs work by having things called


    objects perform actions
    – System.out: an object used for sending output
    to the screen
    • The actions performed by an object are called
    methods
    – println: the method or action that the
    System.out object performs

    9
    BITS Pilani, Pilani Campus
    System.out.println

    • Invoking or calling a method: When an object performs


    an action using a method
    – Also called sending a message to the object
    – Method invocation syntax (in order): an object, a dot (period),
    the method name, and a pair of parentheses
    – Arguments: Zero or more pieces of information needed by the
    method that are placed inside the parentheses

    System.out.println("This is an argument");

    10
    BITS Pilani, Pilani Campus
    class Bicycle {
    int cadence = 0; The Bicycle
    int speed = 0;
    int gear = 1;

    void changeCadence(int newValue) {


    cadence = newValue;
    }
    void changeGear(int newValue) {
    gear = newValue;
    }
    void speedUp(int increment) {
    speed = speed + increment;
    }
    void applyBrakes(int decrement) {
    speed = speed - decrement;
    }
    void printStates() {
    System.out.println(“cadence:” +cadence+ “speed:” +speed+ “gear:”
    +gear);
    }
    } // End of Bicycle
    11
    BITS Pilani, Pilani Campus
    Running Bicycle
    class BicycleDemo {
    public static void main(String[] args) {

    // Create two different Bicycle objects


    Bicycle bike1 = new Bicycle();
    Bicycle bike2 = new Bicycle();

    // Invoke methods on those objects


    bike1.changeCadence(50);
    bike1.speedUp(10);
    bike1.changeGear(2);
    bike1.printStates();

    bike2.changeCadence(50);
    bike2.speedUp(10);
    bike2.changeGear(2);
    bike2.changeCadence(40);
    bike2.speedUp(10);
    bike2.changeGear(3);
    bike2.printStates();
    } 12
    } BITS Pilani, Pilani Campus
    Questions
    1. When you compile a program written in the Java programming language, the
    compiler converts the human-readable source file into platform-independent code that
    a Java Virtual Machine can understand. What is this platform-independent code called?
    Answer: Bytecode

    2. Which of the following is not a valid comment:


    a. /** comment */
    b. /* comment */
    c. /* comment
    d. // comment
    Answer: C

    3. What is the correct signature of the main method?


    Answer: public static void main(String[] args)

    4. When declaring the main method, which modifier must come first, public or static?
    Answer: They can be in either order, but the convention is public static

    5. What parameters does the main method define?


    Answer: The main method defines a single parameter, usually named args, whose type
    is an array of String objects

    13
    BITS Pilani, Pilani Campus
    THANK YOU

    BITS Pilani, Pilani Campus

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