Java do-while Loop

Introduction

The do-while loop is a control flow statement in Java that allows repetitive execution of a block of code. Unlike the while loop, the do-while loop ensures that the block of code is executed at least once before checking the condition. This makes it useful for situations where the code block needs to be executed at least once regardless of the condition. In this chapter, we will explore the syntax, usage, and examples of the do-while loop in Java.

Syntax

The basic syntax of the do-while loop is as follows:

do {
    // code to be executed
} while (condition);

Key Points:

  • The code block inside the do is executed once before the condition is tested.
  • After executing the code block, the condition is evaluated.
  • If the condition is true, the code block is executed again.
  • This process repeats until the condition becomes false.

Example

Let’s consider an example where we use the do-while loop to print numbers from 1 to 5.

Example Code:

public class DoWhileExample {
    public static void main(String[] args) {
        int count = 1;
        do {
            System.out.println("Count: " + count);
            count++;
        } while (count <= 5);
    }
}

Output:

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

Infinite Loop

A do-while loop can become an infinite loop if the condition never becomes false. This can happen if the loop control variable is not updated correctly.

Example of Infinite Loop:

public class InfiniteDoWhileLoopExample {
    public static void main(String[] args) {
        int count = 1;
        do {
            System.out.println("Count: " + count);
            // Missing count++;
        } while (count <= 5);
    }
}

In this example, the count variable is never incremented, so the condition count <= 5 remains true indefinitely, causing an infinite loop.

Using break in do-while Loop

The break statement can be used to exit the loop prematurely, regardless of the condition.

Example with break:

public class BreakInDoWhileExample {
    public static void main(String[] args) {
        int count = 1;
        do {
            if (count == 3) {
                break;
            }
            System.out.println("Count: " + count);
            count++;
        } while (count <= 5);
    }
}

Output:

Count: 1
Count: 2

Using continue in do-while Loop

The continue statement skips the current iteration of the loop and proceeds with the next iteration.

Example with continue:

public class ContinueInDoWhileExample {
    public static void main(String[] args) {
        int count = 1;
        do {
            if (count == 3) {
                count++;
                continue;
            }
            System.out.println("Count: " + count);
            count++;
        } while (count <= 5);
    }
}

Output:

Count: 1
Count: 2
Count: 4
Count: 5

Diagram: Flow Chart of do-while Loop

   Start
     |
[initialize]
     |
  [execute]
     |
[update/check condition]
     |
    / \
  True  False
   /      \
  |        End
  |
[execute]
  |
[update/check condition]
  |
  True/False (loop continues)

Conclusion

The do-while loop is a useful control flow statement in Java that ensures a block of code is executed at least once before checking the condition. This is particularly useful in scenarios where you need the code block to run at least once regardless of the condition. By understanding the syntax and usage of the do-while loop, including how to manage infinite loops and use break and continue statements, you can write more flexible and efficient Java programs.

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