Loops

Comparison of Loops

1. What Are Loops?

Loops are control structures that allow a block of code to be executed repeatedly until a specified condition is met.

2. Types of Loops in Java

1. for Loop
2. while Loop
3. do-while Loop
4. Enhanced for Loop (for-each Loop)

3. for Loop

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

Syntax

for (initialization; condition; update) {
    // Code to be executed in each iteration
}

Example

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

Working

1. Initialization: Executes once before the loop starts (e.g., int i = 1).
2. Condition: Checked before each iteration. If true, the loop runs; if false, the loop exits.
3. Update: Executes after each iteration (e.g., i++).

4. while Loop

The while loop is used when the number of iterations is not known and depends on a condition.

Syntax

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

Example

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

Working

1. The condition is checked before each iteration.
2. If the condition is true, the loop body executes.
3. If the condition is false, the loop terminates.

5. do-while Loop

The do-while loop is similar to the while loop, but it ensures that the loop body executes at least once before the condition is checked.

Syntax

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

Example

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

Working

1. Executes the loop body first.
2. Then checks the condition.
3. Repeats the process if the condition is true.

6. Enhanced for Loop (for-each Loop)

The enhanced for loop is used to iterate over arrays or collections.

Syntax

for (type variable : arrayOrCollection) {
    // Code to execute for each element
}

Example

int[] numbers = {10, 20, 30, 40, 50};
for (int num : numbers) {
    System.out.println(num);
}

Working

1. Iterates through each element in the array or collection.
2. Assigns each element to the loop variable (num in the example).

Control Statements in Loops

Java provides additional control statements to manage the flow of loops:

1. break

• Terminates the loop immediately.

for (int i = 1; i <= 5; i++) {
    if (i == 3) {
        break; // Exit loop when i equals 3
    }
    System.out.println(i);
}

2. continue

• Skips the current iteration and moves to the next one.

for (int i = 1; i <= 5; i++) {
    if (i == 3) {
        continue; // Skip the rest of the code for i = 3
    }
    System.out.println(i);
}

3. return

• Exits from the current method entirely, stopping all loops.

for (int i = 1; i <= 5; i++) {
    if (i == 3) {
        return; // Exits the method
    }
    System.out.println(i);
}

Examples of Nested Loops

Loops can be nested inside one another for multidimensional iterations.

Example: Nested for Loop

for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 2; j++) {
        System.out.println("i = " + i + ", j = " + j);
    }
}

Output:

i = 1, j = 1
i = 1, j = 2
i = 2, j = 1
i = 2, j = 2
i = 3, j = 1
i = 3, j = 2

Infinite Loops

An infinite loop occurs when the termination condition is never met.

Example

while (true) {
    System.out.println("This is an infinite loop.");
}

Use break to terminate infinite loops when needed.

Best Practices for Loops

1. Avoid Infinite Loops: Ensure the condition eventually becomes false.
2. Optimize Performance: Minimize operations inside the loop.
3. Use Enhanced for: When iterating over arrays/collections.
4. Clear Conditions: Ensure loop conditions are readable and maintainable.