The Project | About Us | Contribute | Donations | License

HOME

Loops are fundamental constructs in Java that allow you to execute a block of code repeatedly based on a condition. They are essential for tasks that require repetitive actions, such as iterating over arrays or collections. In this section, we will cover the different types of loops available in Java, their syntax, and practical examples.

Types of Loops in Java

For Loop
While Loop
Do-While Loop
Enhanced For Loop (For-Each Loop)

For Loop

The for loop is used when you know in advance how many times you want to execute a statement or a block of statements. It consists of three parts: initialization, condition, and increment/decrement.

Syntax:

for (initialization; condition; increment/decrement) {
    // Code to be executed
}

Example:

public class ForLoopExample {
    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            System.out.println("Iteration: " + i);
        }
    }
}

Explanation:

Initialization: int i = 0 sets the starting point.
Condition: i < 5 checks if the loop should continue.
Increment: i++ increases the value of i after each iteration.

While Loop

The while loop is used when you do not know in advance how many times you need to execute a block of code. It continues to execute as long as the condition is true.

Syntax:

while (condition) {
    // Code to be executed
}

Example:

public class WhileLoopExample {
    public static void main(String[] args) {
        int i = 0;
        while (i < 5) {
            System.out.println("Iteration: " + i);
            i++;
        }
    }
}

Explanation:

The loop checks the condition i < 5 before each iteration.
The value of i is incremented inside the loop.

Do-While Loop

The do-while loop is similar to the while loop, but it guarantees that the code block will be executed at least once because the condition is checked after the code block is executed.

Syntax:

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

Example:

public class DoWhileLoopExample {
    public static void main(String[] args) {
        int i = 0;
        do {
            System.out.println("Iteration: " + i);
            i++;
        } while (i < 5);
    }
}

Explanation:

The code block is executed first, then the condition i < 5 is checked.
The loop continues as long as the condition is true.

Enhanced For Loop (For-Each Loop)

The enhanced for loop, also known as the for-each loop, is used to iterate over arrays or collections. It simplifies the code and reduces the chance of errors.

Syntax:

for (type variable : array/collection) {
    // Code to be executed
}

Example:

public class ForEachLoopExample {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        for (int number : numbers) {
            System.out.println("Number: " + number);
        }
    }
}

Explanation:

The loop iterates over each element in the array numbers.
The variable number holds the current element in each iteration.

Practical Exercises

Exercise 1: Sum of First 10 Natural Numbers

Task: Write a program to calculate the sum of the first 10 natural numbers using a for loop.

Solution:

public class SumOfNaturalNumbers {
    public static void main(String[] args) {
        int sum = 0;
        for (int i = 1; i <= 10; i++) {
            sum += i;
        }
        System.out.println("Sum of first 10 natural numbers: " + sum);
    }
}

Exercise 2: Print Even Numbers from 1 to 20

Task: Write a program to print all even numbers from 1 to 20 using a while loop.

Solution:

public class EvenNumbers {
    public static void main(String[] args) {
        int i = 1;
        while (i <= 20) {
            if (i % 2 == 0) {
                System.out.println(i);
            }
            i++;
        }
    }
}

Exercise 3: Reverse an Array

Task: Write a program to reverse an array using a for-each loop.

Solution:

public class ReverseArray {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        int[] reversed = new int[numbers.length];
        int j = 0;
        for (int i = numbers.length - 1; i >= 0; i--) {
            reversed[j] = numbers[i];
            j++;
        }
        for (int number : reversed) {
            System.out.println(number);
        }
    }
}

Common Mistakes and Tips

Infinite Loops: Ensure that the loop condition will eventually become false. Otherwise, you may create an infinite loop.
Off-by-One Errors: Be careful with loop boundaries to avoid off-by-one errors.
Enhanced For Loop: Use the enhanced for loop for readability and simplicity when iterating over arrays or collections.

Conclusion

In this section, we covered the different types of loops in Java, including for, while, do-while, and enhanced for loops. We also provided practical examples and exercises to help you understand how to use loops effectively. Mastering loops is essential for writing efficient and concise code in Java. In the next section, we will explore switch statements, which provide an alternative to using multiple if-else conditions.

Loops

Types of Loops in Java

For Loop

While Loop

Do-While Loop

Enhanced For Loop (For-Each Loop)

Practical Exercises

Exercise 1: Sum of First 10 Natural Numbers

Exercise 2: Print Even Numbers from 1 to 20

Exercise 3: Reverse an Array

Common Mistakes and Tips

Conclusion

Java Programming Course

Module 1: Introduction to Java

Module 2: Control Flow

Module 3: Object-Oriented Programming

Module 4: Advanced Object-Oriented Programming

Module 5: Data Structures and Collections

Module 6: Exception Handling

Module 7: File I/O

Module 8: Multithreading and Concurrency

Module 9: Networking

Module 10: Advanced Topics

Module 11: Java Frameworks and Libraries

Module 12: Building Real-World Applications