Java - while Loop

Java while Loop

Java while loop statement repeatedly executes a code block as long as a given condition is true.

The while loop is an entry control loop, where conditions are checked before executing the loop's body.

Syntax of while Loop

The syntax of a while loop is −

while(Boolean_expression) {
   // Statements
}

Execution Process of a while Loop

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

The following diagram shows the flow diagram (execution process) of a while loop in Java -

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.

Examples of while Loop

Example 1: Printing Numbers in a Range Using while Loop

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: Printing Elements of an Array Using while Loop

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 size 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

Infinite While Loop

You can implement an infinite while loop using the while loop statement by providing "true" as the test condition.

Example: Implementing Nested while Loop

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