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1. Introduction
In Java, loops are used to execute a set of statements repeatedly until a particular condition is satisfied. The while loop and the do-while loop are two forms of conditional loops that serve this purpose.
A while loop evaluates its expression at the beginning of each loop cycle, so the code inside the loop may not execute at all if the condition is not met.
A do-while loop evaluates its expression at the end of each loop cycle, which guarantees that the code inside the loop will execute at least once.
2. Key Points
1. A while loop checks the condition before the code within the loop is executed.
2. A do-while loop checks the condition after the code within the loop is executed.
3. As a result of the check timing, a while loop may not execute its code at all if the condition is initially false.
4. A do-while loop always executes its code block at least once.
3. Differences
| while loop | do-while loop |
|---|---|
| The while loop checks the condition at the beginning of the loop. | The do-while loop checks the condition at the end of the loop. |
| If the condition is false at the first iteration, the loop body does not execute even once. | The loop body is guaranteed to execute at least once, regardless of the condition. |
| More commonly used when the number of iterations is unknown and depends solely on the condition. | More suitable when the loop body needs to be executed at least once, such as when displaying a menu or prompting for user input. |
| If the condition is initially false, It can result in zero loop iterations. | Always results in at least one iteration, even if the condition is initially false. |
| Syntax: while (condition) { statements; } | Syntax: do { statements; } while (condition); |
4. Example
public class LoopComparison {
public static void main(String[] args) {
int count = 0;
// Step 1: Using a while loop
System.out.println("while loop output:");
while (count < 0) {
System.out.println("This will not print");
}
// Step 2: Using a do-while loop
System.out.println("do-while loop output:");
do {
System.out.println("This will print at least once");
count++;
} while (count < 0);
}
}
Output:
while loop output: do-while loop output: This will print at least once
Explanation:
1. The while loop with the condition count < 0 does not execute because the condition is false at the start.
2. The do-while loop, on the other hand, executes once before checking the condition count < 0, which is why the statement within the loop's body is printed.
5. When to use?
- Use a while loop when you want to execute code only if the condition is true at the start of the loop.
- Use a do-while loop when you want to ensure that the code within the loop executes at least once, regardless of the condition being true or false.
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