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Java Basics
CHAPTER 08 Beginner

Loops in Java

Updated: May 17, 2026
5 min read

# CHAPTER 8

Loops in Java

1. Introduction

Loops let you execute a block of code repeatedly. Instead of writing System.out.println() 100 times, you write one loop. Loops are the workhorse of programming — processing lists, iterating through databases, and running game engines.

2. Learning Objectives

  • Use for, while, and do-while loops.
  • Control flow with break and continue.
  • Write nested loops.
  • Build a multiplication table generator.

3. The for Loop

Best when you know exactly how many times to iterate.
java
1234 
for (int i = 1; i <= 5; i++) {
    System.out.println("Count: " + i);
}
// Output: Count: 1, Count: 2, Count: 3, Count: 4, Count: 5

Structure: for (initialization; condition; update) { body }

4. The while Loop

Best when you don't know how many iterations in advance.
java
12345 
int count = 1;
while (count <= 5) {
    System.out.println("Count: " + count);
    count++;
}

5. The do-while Loop

Guarantees the body executes at least once.
java
123456 
int num = 10;
do {
    System.out.println("Number: " + num);
    num++;
} while (num <= 5);
// Prints "Number: 10" even though 10 > 5

6. Enhanced for-each Loop

Simplified syntax for iterating over arrays and collections.
java
1234 
int[] scores = {90, 85, 78, 92, 88};
for (int score : scores) {
    System.out.println("Score: " + score);
}

7. break and continue

  • break: Immediately exits the entire loop.
  • continue: Skips the current iteration and jumps to the next one.
java
1234567891011 
for (int i = 1; i <= 10; i++) {
    if (i == 5) break;       // Stop at 5
    System.out.print(i + " ");
}
// Output: 1 2 3 4

for (int i = 1; i <= 10; i++) {
    if (i % 2 == 0) continue; // Skip even numbers
    System.out.print(i + " ");
}
// Output: 1 3 5 7 9

8. Nested Loops

java
123456 
for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 3; j++) {
        System.out.print("(" + i + "," + j + ") ");
    }
    System.out.println();
}

9. Mini Project: Multiplication Table Generator

java
123456789101112131415 
import java.util.Scanner;

public class MultiplicationTable {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = sc.nextInt();

        System.out.println("\n=== Multiplication Table for " + num + " ===");
        for (int i = 1; i <= 12; i++) {
            System.out.printf("%d x %2d = %3d%n", num, i, num * i);
        }
        sc.close();
    }
}

10. Infinite Loop

java
123 
while (true) {
    // Runs forever until break or program termination
}

11. Common Mistakes

  • Off-by-one errors: Using < vs <= incorrectly.
  • Infinite loops: Forgetting to update the loop variable in a while loop.
  • Modifying the loop variable inside the body: Can cause unexpected behavior.

12. MCQ Quiz with Answers

Question 1

Which loop always executes at least once?

Question 2

What does break do?

Question 3

What does continue do?

Question 4

How many times does for(int i=0; i<5; i++) iterate?

Question 5

What is the for-each loop used for?

Question 6

What causes an infinite loop?

Question 7

Nested loops are:

Question 8

for(;;) creates:

Question 9

What is the output of for(int i=0; i<3; i++) { System.out.print(i); }?

Question 10

Which loop checks condition AFTER execution?

13. Interview Questions

  • Q: What is the difference between while and do-while?
  • Q: How do you avoid infinite loops?
  • Q: When should you use for vs while?
  • Q: Can break exit nested loops? (Answer: only the innermost one, use labeled break for outer)

14. Summary

Java provides for, while, do-while, and enhanced for-each loops. break exits loops, continue skips iterations. Nested loops create multi-dimensional patterns. Always ensure loop termination conditions to avoid infinite loops.

15. Next Chapter Recommendation

In Chapter 9: Arrays in Java, we'll learn how to store and manipulate collections of data efficiently.

Finish this Chapter

Save your progress on your learning path and prepare for coding interview challenges.

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Next Chapter Arrays in Java

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