Which loop to use when

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Java provides three primary looping constructs—while, do-while, and for—and an additional enhanced loop (for-each) for collections.
Understanding when to use each loop helps you write clearer and more efficient code.

Choosing the right loop depends on whether you know the number of repetitions and how the loop condition behaves.

1. For Loop

Use the for loop when you know exactly how many times the loop should run.

It combines initialization, condition, and update in one line, making it ideal for loops that count or iterate in a predictable manner.

for (int i = 1; i <= 10; i++) {
    System.out.println(i);
}

When to use a for loop?

• When the number of iterations is fixed or easily calculated
• When using a counter/index
• When iterating through a range of numbers
• When writing compact, structured loops

Common examples:

• Printing a list of numbers
• Running a loop a fixed number of times
• Nested loops for patterns or tables

2. While Loop

Use the while loop when the number of iterations is not known beforehand. The loop continues as long as the condition remains true.

int i = 1;
while (i <= 10) {
    System.out.println(i);
    i++;
}

When to use a while loop?

• When the loop depends on changing conditions
• When you may not enter the loop at all
• When input, file reading, or dynamic conditions control the loop

Practical examples:

• Waiting for user input
• Reading data from a file until the end
• Continuously checking a sensor value

3. Do-While Loop

A do-while loop is similar to a while loop, but with one important difference: It executes at least once, even if the condition is false from the start.

int i = 11;
do {
    System.out.println(i);   // executes once
    i++;
} while (i <= 10);

When to use a do-while loop?

• When a task must run at least once
• When the loop condition is checked after execution
• When designing menu-driven or input-driven programs

Real-world use:

• ATM menu
• Game menus
• Asking user “Do you want to continue?”

4. Enhanced For Loop (for-each)

The enhanced for loop (also called for-each) is used to iterate through arrays or collections without needing an index.

int[] nums = {10, 20, 30};
for (int n : nums) {
    System.out.println(n);
}

When to use for-each?

• When you want to access every element directly
• When you don't need the index
• When working with arrays, lists, sets, maps (keys or values)

It improves readability and reduces the chance of index errors.

Summary Table

Golden Rule

• Use for → when you know how many times
• Use while → when you know until when
• Use do-while → when it must run at least once
• Use for-each → when working with collections/arrays

These rules make it easy to choose the right loop for any situation.