Loop and Array

Loop
• In programming languages, loops are used to execute a set of

instructions/functions repeatedly when some conditions
become true. There are three types of loops in java.
• for loop
• while loop
• do-while loop
Java For Loop
The simple for loop is same as C/C++. We can initialize variable,

check condition and increment/decrement value.
Syntax:
for(initialization;condition;incr/decr)
{
//code to be executed
}
class ForExample
{
public static void main(String[] args)
{
for(int i=1;i<=10;i++)
{
System.out.println(i);
}
}
}
• If you use two semicolons ;; in the for loop, it will be
infinitive for loop.
for(;;)
{
}
Java While Loop
• The Java while loop is used to iterate a part of the program

several times. If the number of iteration is not fixed, it is
recommended to use while loop.
while(condition)
{
}
class WhileExample
{
{
int i=1;
while(i<=10)
{
i++;
}
}
}
If you pass true in the while loop, it will be infinitive while loop.
while(true)
{
}
Java do-while Loop
do
{
}while(condition);
class DoWhileExample
{
{
int i=1;
do
{
i++;
}while(i<=10);
}
}
Java Break Statement
• The Java break is used to break loop or switch statement. It breaks the current flow of
the program at specified condition. In case of inner loop, it breaks only inner loop.
class BreakExample
{
{
{
if(i==5)
break;
}
}
}
Java Continue Statement
• The Java continue statement is used to continue loop. It continues the current flow of the
program and skips the remaining code at specified condition. In case of inner loop, it
continues only inner loop.
class ContinueExample
{
{
{
if(i==5)
continue;
}
}
}
Java Array
• Normally, array is a collection of similar type of elements that

have contiguous memory location.
• Java array is an object the contains elements of similar data
type. It is a data structure where we store similar elements.
• Array in java is index based, first element of the array is stored
at 0 index.
• Types of Array in java
• There are two types of array.
• Single Dimensional Array
• Multidimensional Array
Single Dimensional Array in java
Syntax to Declare an Array in java

dataType[] arr; (or)
dataType []arr; (or)
dataType arr[];
• Instantiation of an Array in java
arrayRefVar=new datatype[size];
class Testarray{
public static void main(String args[])
{

int a[]=new int[5];//declaration and instantiation
a[0]=10;//initialization
a[1]=20;
a[2]=70;
a[3]=40;
a[4]=50;

for(int i=0;i<a.length;i++)
System.out.println(a[i]);

}
}
class Testarray1
{
{

int a[]={33,3,4,5};//declaration, instantiation and initialization

//printing array
for(int i=0;i<a.length;i++)//length is the property of array
System.out.println(a[i]);

}
}
Multidimensional array in java
• Syntax to Declare Multidimensional Array in java

 dataType[][] arrayRefVar; (or)
 dataType [][]arrayRefVar; (or)
 dataType arrayRefVar[][]; (or)
 dataType []arrayRefVar[];
• int[][] arr=new int[3][3];//3 row and 3 column
arr[0][0]=1;
arr[0][1]=2;
arr[0][2]=3;
arr[1][0]=4;
arr[1][1]=5;
arr[1][2]=6;
arr[2][0]=7;
arr[2][1]=8;
arr[2][2]=9;
int[][] a = new int[3][4];
class Testarray
{
{
//creating two matrices
int a[][]={{1,3,4},{3,4,5}};
int b[][]={{1,3,4},{3,4,5}};

//creating another matrix to store the sum of two matrices
int c[][]=new int[2][3];

//adding and printing addition of 2 matrices
for(int i=0;i<2;i++)
{
for(int j=0;j<3;j++)
{
c[i][j]=a[i][j]+b[i][j];
System.out.print(c[i][j]+" ");
}
System.out.println();//new line
}

}
}
Irregular arrays or Jagged arrays
• A jagged array in Java is a collection of arrays where each array may
contain a varied number of elements.
• Jagged arrays are also known as "ragged arrays" or "irregular arrays".
• A jagged array is sometimes called an "array of arrays."
Declaration and Initialization of Jagged array

Datatype arrayName[][] = new datatype[numRows][];
arrayName[0] = new datatype[numColumns1];
arrayName[1] = new datatype[numColumns2];
...
Example:
#syntax
int[][] jaggedArray = new int[3][];
#initialize column elements

jaggedArray[0] = new int[5];
#initialize the values
jaggedArray[0] = new int[] { 1, 3, 5, 7, 9 };
jaggedArray[1] = new int[] { 0, 2, 4, 6 };
jaggedArray[2] = new int[] { 11, 22 };
1 3 5 7 9
0 2 4 6
11 12
int[][] a = {
{1, 2, 3},
{4, 5, 6, 9},
{7},
};
class MultidimensionalArray {
public static void main(String[] args) {
// create a 2d jagged array directly

int[][] a = {
{1, 2, 3},
{4, 5, 6, 9},
{7},
};
// calculate the length of each row

System.out.println("Length of row 1: " + a[0].length);
}
}
Assigning Array References
• When you assign one array reference variable to another, you are simply changing what object that variable
refers to.
class Arrayref
{
{
int a[]={1,2,3,4,5};
int b[]={3,4,5,6,7};
a=b; //assigning array reference
b[3]=20;
System.out.print(i);
Output: 3 4 5 20 7
Java For-each Loop | Enhanced For Loop
• It is mainly used to traverse the array or collection elements.

class Foreachloop
{
{
int a[]={1,2,3,4,5};
for(int i:a)
System.out.print(i);

Loop and Array

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Loop

• In programming languages, loops are used to execute a set of

The simple for loop is same as C/C++. We can initialize variable,

• The Java while loop is used to iterate a part of the program

• Normally, array is a collection of similar type of elements that

Syntax to Declare an Array in java

• Syntax to Declare Multidimensional Array in java

Declaration and Initialization of Jagged array

#initialize column elements

// create a 2d jagged array directly

// calculate the length of each row

• It is mainly used to traverse the array or collection elements.

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