P 3- Looping

Looping in Java (In-Depth Guide) Looping is a fundamental concept in Java (and programming in general) that allows you to execute a block of code repeatedly based on a condition. Java provides several looping mechanisms, each suited for different scenarios. 1. for Loop The for loop is used when the number of iterations is known beforehand. Syntax for (initialization; condition; update) { // Code to execute } Example for (int i = 1; i

Apr 7, 2025 - 16:27

Looping in Java (In-Depth Guide)

Looping is a fundamental concept in Java (and programming in general) that allows you to execute a block of code repeatedly based on a condition. Java provides several looping mechanisms, each suited for different scenarios.

1. `for` Loop

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

Syntax

for (initialization; condition; update) {
    // Code to execute
}

Example

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

Output:

Iteration: 1
Iteration: 2
Iteration: 3
Iteration: 4
Iteration: 5

Variations

a) Enhanced `for` Loop (for-each)

Used for iterating over arrays and collections.

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

Output:

b) Infinite `for` Loop

for (;;) {
    System.out.println("This runs forever!");
}

2. `while` Loop

The while loop executes as long as the condition is true. It is used when the number of iterations is not known in advance.

Syntax

while (condition) {
    // Code to execute
}

Example

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

Output:

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

Infinite `while` Loop

while (true) {
    System.out.println("Infinite loop!");
}

3. `do-while` Loop

Similar to while, but guarantees at least one execution before checking the condition.

Syntax

do {
    // Code to execute
} while (condition);

Example

int x = 5;
do {
    System.out.println("x = " + x);
    x--;
} while (x > 0);

Output:

x = 5
x = 4
x = 3
x = 2
x = 1

4. Nested Loops

A loop inside another loop is called a nested loop.

Example (Printing a Pyramid)

for (int i = 1; i <= 5; i++) {
    for (int j = 1; j <= i; j++) {
        System.out.print("* ");
    }
    System.out.println();
}

Output:

* 
* * 
* * * 
* * * * 
* * * * *

5. Loop Control Statements

Java provides keywords to alter loop execution:

Keyword	Description
`break`	Exits the loop immediately
`continue`	Skips the current iteration and moves to the next
`return`	Exits the entire method

Example: `break`

for (int i = 1; i <= 10; i++) {
    if (i == 6) {
        break; // Exit loop when i=6
    }
    System.out.println(i);
}

Output:

Example: `continue`

for (int i = 1; i <= 5; i++) {
    if (i == 3) {
        continue; // Skip iteration when i=3
    }
    System.out.println(i);
}

Output:

6. Best Practices for Loops

Avoid infinite loops unless intentional (e.g., in servers).
Use for when the number of iterations is known.
Use while when the condition is dynamic.
Prefer for-each for collections (cleaner syntax).
Keep loop bodies small for readability.
Use break and continue sparingly (can make code harder to debug).

Conclusion

for loop → Best for fixed iterations.
while loop → Best for unknown iterations.
do-while loop → Ensures at least one execution.
Nested loops → Useful for multi-dimensional data.
break & continue → Control loop flow.

Mastering loops is essential for efficient iteration in Java programs.