Loops in Java – for, while, do-while, and Enhanced for-loop

Loops are fundamental in Java programming. They allow you to execute a block of code repeatedly until a condition is met, making programs efficient and dynamic.

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🔍 Why Loops are Important?

• Automate repetitive tasks.
• Reduce code duplication.
• Essential for working with arrays, collections, and algorithms.
• Widely used in real-world Java projects and interviews.

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✅ for Loop

The for loop is used when the number of iterations is known beforehand.

✅ Syntax:

for(initialization; condition; update) {
    // Code block
}

✅ Example:

for(int i = 1; i <= 5; i++) {
    System.out.println("Iteration: " + i);
}

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✅ while Loop

The while loop is used when the number of iterations is unknown and depends on a condition.

✅ Syntax:

while(condition) {
    // Code block
}

✅ Example:

int count = 1;
while(count <= 5) {
    System.out.println("Count: " + count);
    count++;
}

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✅ do-while Loop

The do-while loop executes the block at least once, even if the condition is false.

✅ Syntax:

do {
    // Code block
} while(condition);

✅ Example:

int num = 1;
do {
    System.out.println("Number: " + num);
    num++;
} while(num <= 5);

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✅ Enhanced for Loop (for-each)

Introduced in Java 5, the enhanced for loop simplifies iteration over arrays and collections.

✅ Example:

int[] numbers = {1, 2, 3, 4, 5};
for(int n : numbers) {
    System.out.println("Value: " + n);
}

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🔄 Performance & When to Use

• for loop: Best for indexed iterations or when count is known.
• while loop: Ideal when condition-driven repetition is needed.
• do-while: Use when block must execute at least once.
• enhanced for: Best for arrays and collections without index operations.

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🚫 Common Mistakes

• Infinite loops due to missing update or wrong condition.
• Modifying a collection inside an enhanced for-loop.
• Using while when index-based iteration is required.

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💡 Tips & Best Practices

• Use descriptive loop variables.
• Keep loop logic minimal and avoid heavy operations inside.
• Use break and continue wisely to control flow.
• Prefer enhanced for-loop for read-only iteration of collections.

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🧠 Interview Relevance

• Q: Difference between for and while loop?

• A: for is count-controlled; while is condition-controlled.

• Q: When to use enhanced for loop?

• A: When iterating through arrays or collections without modifying them.

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🧩 Java Version Relevance

Java Version	Feature
Java 1.0	Introduced for, while, do-while loops
Java 5	Added enhanced for loop for collections and arrays

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✅ Summary

• for: Use for fixed iterations.
• while: Use for condition-driven iterations.
• do-while: Ensures at least one execution.
• enhanced for: Simplifies array and collection traversal.

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