Loops in Java

AAYUSH SHARMA February 02, 2021

Looping is a feature in a programming language that provides you the facility to run a set of instructions/functions repeatedly under some conditions.

In java, there are three ways to execute the loops. All the ways are similar in terms of basic functionalities but they are different in terms of syntax and checking time.

1. while loop: 

While loop is a control flow statement that allows the code to execute the flow of statement repeatedly according to the Boolean conditions.

Syntax:

while (boolean condition)
{
   loop statements...
}

Flowchart:


Loops in Java

  • While loop starts by checking the given condition first. If the given condition is true, then the statements in the loop executed else the first statement following the loop will be executed. That's why it calls an Entry control Loop.


  • When the condition is checked and true, all the statements inside the loop body are executed.


  • When the condition becomes false, then the loop will be terminated and end the cycle.

fil

Example


// Java Program to illustrate while loop
public class while1 {
   public static void main (String args[]){

      // Defining variable
   int n=1;

   // Exit when n becomes greater than 10
   while (n<=10)
   {
      System.out.println( "Value of n: "+n);
      //Increment the value of n for next iteration
      n++;
   }
}
}


Output

Value of n: 1

Value of n: 2

Value of n: 3

Value of n: 4

Value of n: 5

Value of n: 6

Value of n: 7

Value of n: 8

Value of n: 9

Value of n: 10

2. for loop: 

In Java for loop is a control flow statement which iterates the part of the programs multiple times. A for statement contains the initialization, condition, and increment/decrement which is shorter and easy to debug.

Syntax:

for (initialization condition; testing condition; 
                              increment/decrement)
{
    statement(s)
}

 Flowchart:

Loops in Java

Example

class forLoopDemo 
{ 
    public static void main(String args[]) 
    { 
        // for loop begins when x=2 
        // and runs till x <=4 
        for (int x = 1; x <= 5; x++) 
            System.out.println("Value of x:" + x); 
    } 
} 

Output

Value of x:1

Value of x:2

Value of x:3

Value of x:4

Value of x:5

                                                Enhanced For loop

In java 5, Java introduced another version of for loop. Enhanced for loop gives a simple way to iterate through the elements of collection or array. It should be used only when there is a need for iteration through the elements in a sequential manner without knowing the index.

Syntax

public for (T element:Collection obj/array)
{
    statement(s)
}

Example

// Java program to illustrate enhanced for loop 
public class enhancedloop 
{ 
    public static void main(String args[]) 
    { 
        String array[] = {"Sam", "Henry", "Dom"}; 
  
        //enhanced for loop 
        for (String x:array) 
        { 
            System.out.println(x); 
        } 
  
        /* for loop for same function 
        for (int i = 0; i < array.length; i++) 
        { 
            System.out.println(array[i]); 
        } 
        */
    } 
} 

Output

Sam

Henry

Dom


3. do-while: 

The only difference between the while loop and the do-while loop, do-while loop check the condition after executing the statements. It is also an example of the Exiting control loop. 

Syntax

do
{
    statements..
}
while (condition);

Flowchart


Loops in Java

Example


// Java program to illustrate do-while loop 
class dowhileloop
{ 
    public static void main(String args[]) 
    { 
        int x = 21; 
        do
        { 
            // The line will be printed even 
            // if the condition is false 
            System.out.println("Value of x:" + x); 
            x++; 
        } 
        while (x < 15); 
    } 
} 


Output

Value of x: 21
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