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A loop statement allows a program to execute a statement(s) multiple times which provides easier and flexible programming. Java has three loop statements:

  • while loop
  • do-while loop
  • for loop

The While Loop:

A while loop allows a set of statements to be executed repeatedly until a given condition is true. The while loop can be viewed as a repeating if statement.

Syntax

while (condition) {
      statements;
    }

Flow Diagram:

Java While Loop

In below mentioned example, program uses while loop to sum all integers from 1 to 5.

public class MyClass {
  public static void main(String[] args) {
    int i = 0;
    int sum = 0;
    while (i <= 5) {
      sum = sum + i;
      i++;
    }
    System.out.println(sum);  
  }
}

The output of the above code will be:

15

The Do-While Loop:

The do-while loop is a variant of while loop which execute statements before checking the conditions. Therefore the do-while loop executes statements at least once.

Syntax

do {
  statements;
}
while (condition);

Flow Diagram:

Java Do-While Loop

In the below example, even if the condition is not fulfilled, the do-while loop executes the statements once.

public class MyClass {
  public static void main(String[] args) {
    int i = 10;
    int sum = 0;
    do{
        sum = sum + i;
        i = i+1;
    }
    while (i <= 5);
    System.out.println(sum);  
  }
}

The output of the above code will be:

10