Loops in Java

Loops are used in programming to execute a block of code repeatedly as long as a specified condition remains true. They help reduce code duplication and make it easier to traverse data structures.

Java provides four main types of loops:

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

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1. The for Loop

The for loop is ideal when you know in advance how many times the loop should run.

Syntax:

for (initialization; condition; update) {
    // code block to be executed
}

Example:

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

• Initialization: Executes once before the loop starts.
• Condition: Evaluated before every iteration. If true, the loop body runs.
• Update: Executes after the loop body has run, usually incrementing or decrementing the loop control variable.

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2. The while Loop

The while loop runs code as long as a specified condition evaluates to true. Use this when you do not know the exact number of iterations beforehand.

Syntax:

while (condition) {
    // code block to be executed
    // increment/decrement or update condition
}

Example:

int count = 1;
while (count <= 5) {
    System.out.println("Count: " + count);
    count++; // Critical: update statement to avoid infinite loop
}

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3. The do-while Loop

The do-while loop is a variant of the while loop. The key difference is that it executes the code block once before checking if the condition is true. It then repeats the loop as long as the condition remains true.

Syntax:

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

Example:

int number = 10;
do {
    System.out.println("Number is: " + number);
    number++;
} while (number < 5); // Condition is false, but code runs once

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4. The Enhanced for-each Loop

The for-each loop is designed specifically to iterate through arrays or collections. It is cleaner and less error-prone because you don’t have to manage loop indices.

Syntax:

for (type variableName : arrayName) {
    // code block to be executed
}

Example:

String[] programmingLanguages = {"Java", "Python", "JavaScript", "C++"};

for (String language : programmingLanguages) {
    System.out.println("Language: " + language);
}

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Loop Control Statements

Java provides two keyword statements to control the flow of loops: break and continue.

1. The break Statement

The break statement is used to jump out of/terminate a loop prematurely, regardless of whether the loop condition is met.

for (int i = 1; i <= 10; i++) {
    if (i == 5) {
        break; // exits the loop when i is 5
    }
    System.out.println(i);
}
// Output: 1, 2, 3, 4

2. The continue Statement

The continue statement skips the current iteration and jumps directly to the next iteration of the loop (evaluating the loop update and condition).

for (int i = 1; i <= 5; i++) {
    if (i == 3) {
        continue; // skips the rest of the loop block for i = 3
    }
    System.out.println(i);
}
// Output: 1, 2, 4, 5

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Infinite Loops

An infinite loop occurs when a loop’s condition never becomes false. This can crash your application or consume excessive CPU resources.

Example of an Infinite Loop:

// ❌ Dangerous: This runs forever
while (true) {
    System.out.println("Infinite loop!");
}

[!CAUTION] Always ensure that your loop has a clear exit condition (e.g., the loop variable is incremented/decremented properly, or a break statement is reached).

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Next Steps ➡️

Now that you can repeat tasks using loops, the next topic will cover Methods (Functions) to organize and reuse your Java code.