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Java - while Loop


A while loop statement in Java programming language repeatedly executes a target statement as long as a given condition is true.

Syntax

The syntax of a while loop is −

while(Boolean_expression) {
   // Statements
}

Here, statement(s) may be a single statement or a block of statements. The condition may be any expression, and true is any non zero value.

When executing, if the boolean_expression result is true, then the actions inside the loop will be executed. This will continue as long as the expression result is true.

When the condition becomes false, program control passes to the line immediately following the loop.

Flow Diagram

Java While Loop

Here, key point of the while loop is that the loop might not ever run. When the expression is tested and the result is false, the loop body will be skipped and the first statement after the while loop will be executed.

Example 1

In this example, we're showing the use of a while loop to print numbers starting from 10 to 19. Here we've initialized an int variable x with a value of 10. Then in while loop, we're checking x as less than 20 and within while loop, we're printing the value of x and incrementing the value of x by 1. While loop will run until x becomes 20. Once x is 20, loop will stop execution and program exits.

public class Test {

   public static void main(String args[]) {
      int x = 10;

      while( x < 20 ) {
         System.out.print("value of x : " + x );
         x++;
         System.out.print("\n");
      }
   }
}

Output

value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19

Example 2

In this example, we're showing the use of a while loop to print contents of an array. Here we're creating an array of integers as numbers and initialized it some values. We've created a variable named index to represent index of the array while iterating it. In while loop we're checking the index to be less than size of the array and printed the element of the array using index notation. index variable is incremented by 1 and loop continues till index becomes the sie of the array and loop exits.

public class Test {

   public static void main(String args[]) {
      int [] numbers = {10, 20, 30, 40, 50};
      int index = 0;

      while( index < 5 ) {
         System.out.print("value of item : " + numbers[index] );
         index++;
         System.out.print("\n");
      }
   }
}

Output

value of item : 10
value of item : 20
value of item : 30
value of item : 40
value of item : 50

Example 3

In this example, we're showing the infinite loop using while loop. It will keep printing the numbers until you press ctrl+c to terminate the program.

public class Test {

   public static void main(String args[]) {
      int x = 10;

      while( true ) {
         System.out.print("value of x : " + x );
         x++;
         System.out.print("\n");
      }
   }
}

Output

value of item : 10
value of item : 20
value of item : 30
value of item : 40
value of item : 50
...
ctrl+c
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