In this article, you will learn about the do-while loop and how to create do-while loop in Java programming.
Loops in Java are used when we want to execute a block of statements repeatedly until a specific condition is met(condition is false).
Java do-while Loop
Java do-while loop is an exit-control loop, which means unlike while loop, a do-while loop check for the condition after executing the statements or the loop body.
The do-while loop is similar to while loop with one main difference. The body of the do-while loop is executed at least once before the test-expression is checked.
Note: the do-while loop will execute the statements at least once before any condition is checked.
Syntax
do {
//body of the loop
//statements to be executed
}
//test expression is a boolean expression
while (test_expression);
Flowchart of do-while loop
How do-while loop works?
When the Control falls into the do-while loop, it first executes the body of the loop inside the do block and then it checks the test_expression.
If the test expression is evaluated to true,
- The statements inside the do block(body of the loop) get executed.
- Then, the test expression is evaluated again and this process goes on until the test expression is evaluated to false.
If the test expression is evaluated to false,
- do-while loop gets terminated and control goes out of the do-while loop.
Example 1
public class DoWhileLoopDemo {
public static void main(String[] args) {
int i = 1;
do {
System.out.println("value of i: " + i);
//increment value of i by 1
i++;
}
//exit when i becomes greater than 3
while (i < 4);
}
}
Output
value of i: 1 value of i: 2 value of i: 3
Example explained
In the above example,
1. i is initialized with value 1.
2. Execute the loop body inside do block.
“value of i: 1” gets printed.
- Updation is done. Now i = 2.
3. Condition 2 < 4 is checked, yields true.
4. Execute the loop body inside do block.
- “value of i: 2” gets printed.
- Updation is done. Now i = 3.
5. Condition 3< 4 is checked, yields true.
6. Execute the loop body inside do block.
- “value of i: 3” gets printed.
- Updation is done. Now i = 4.
7. Condition 4< 4 is checked, yields false.
8. Exit from the do-while loop.
Example 2
The below program will print the sum of natural numbers from 1 to 10.
public class DoWhileLoopDemo {
public static void main(String[] args) {
int i = 1, sum = 0;
do {
sum = sum + i;
//Increment the value of i for
//next iteration
i++;
}
// Exit when i becomes greater than 10
while (i <= 10);
System.out.println("Sum of numbers from 1 to 10: " + sum);
}
}
Output
Sum of numbers from 1 to 10: 55