In Java, both the while loop and the do-while loop are used to execute code multiple times, but they differ in terms of when the loop condition is checked. Let’s explore the differences and when each loop is useful.
While Loop
The while loop checks the condition before executing the loop body. If the condition is false initially, the loop won’t run at all.
Syntax:
while (condition) {
// Code to execute
}
Example:
int i = 1;
while (i <= 5) {
System.out.println(i);
i++;
}
In this example, the loop prints the numbers 1 to 5, as long as the condition i <= 5 is true.
Do-While Loop
The do-while loop checks the condition after executing the loop body. This ensures that the loop runs at least once, even if the condition is false initially.
Syntax:
do {
// Code to execute
} while (condition);
Example:
int i = 1;
do {
System.out.println(i);
i++;
} while (i <= 5);
In this case, the loop will print the numbers 1 to 5, but it guarantees one execution of the loop body before checking the condition.
Key Differences
| While Loop | Do-While Loop |
|---|---|
| Condition is checked first | Condition is checked after loop |
| May not execute if condition is false | Always executes at least once |
| Used when we are unsure if the loop should run | Used when we want the loop to run at least once |
Example: When to Use While Loop
int num = 10;
while (num > 0) {
System.out.println(num);
num--;
}
The while loop is useful when we don’t know how many times we need to iterate, but we want the loop to stop as soon as the condition is false.
Example: When to Use Do-While Loop
int num = 10;
do {
System.out.println("Number is " + num);
num--;
} while (num > 0);
This loop guarantees that the message is printed at least once, even if num starts with a value that does not meet the condition.
Use Cases
- While Loop: Ideal for situations where we want to check a condition before every iteration. For example, reading input until a specific condition is met.
- Do-While Loop: Suitable when we want to ensure the code runs at least once before checking a condition. For example, prompting a user to input data at least once, even if the data is invalid initially.
Conclusion
While both while and do-while loops are essential for repetitive tasks in Java, the choice between them depends on when we need the condition to be checked—either before or after running the loop body. For more detailed information, refer to the official Java documentation.
