Java Control Flow Statements:

if-else, else-if, switch, and Loops

Control flow statements in Java determine how the program's execution flows based on conditions or repeated actions. In this post, we’ll explore conditional branching (if, else if, else, switch) and looping constructs (for, while, do-while) in Java, with detailed examples and code comments for better understanding.

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Conditional Statements in Java

if Statement

The if statement executes a block only when the given condition evaluates to true.

javaCopyEditint number = 5;

// Check if the number is greater than 0
if (number > 0) {
    System.out.println("Positive number"); // This line will execute
}

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if-else Statement

Use if-else to handle two possibilities.

javaCopyEditint number = -3;

// Check if the number is non-negative
if (number >= 0) {
    System.out.println("Positive or Zero");
} else {
    System.out.println("Negative number"); // This line will execute
}

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else-if Ladder

The else-if ladder allows checking multiple conditions in sequence.

javaCopyEditint marks = 75;

if (marks >= 90) {
    System.out.println("Grade A");
} else if (marks >= 75) {
    System.out.println("Grade B"); // This line will execute
} else if (marks >= 60) {
    System.out.println("Grade C");
} else {
    System.out.println("Grade D");
}

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switch Statement

A cleaner alternative to multiple if-else conditions when comparing the same variable against multiple constant values.

javaCopyEditint day = 3;

switch (day) {
    case 1:
        System.out.println("Monday");
        break; // Exit switch after matching case
    case 2:
        System.out.println("Tuesday");
        break;
    case 3:
        System.out.println("Wednesday"); // This line will execute
        break;
    default:
        System.out.println("Invalid day"); // Executed if no case matches
        break;
}

Note: Without break, control falls through to the next case.

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Looping Constructs in Java

for Loop

Use this when you know how many times to repeat.

javaCopyEdit// Print numbers from 0 to 4
for (int i = 0; i < 5; i++) {
    System.out.println("Iteration " + i); // Runs 5 times
}

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while Loop

Use when the number of repetitions is unknown and depends on a condition.

javaCopyEditint i = 0;

// Loop while i is less than 5
while (i < 5) {
    System.out.println("While loop: " + i);
    i++; // Increment to avoid infinite loop
}

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do-while Loop

Executes the loop body at least once, even if the condition is false initially.

javaCopyEditint i = 0;

do {
    System.out.println("Do-while loop: " + i); // Always executes once
    i++;
} while (i < 5);

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Choosing the Right Loop

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Common Mistakes and Tips

• Uninitialized local variables in conditional blocks may cause compile-time errors.

• Omitting the break in a switch can lead to fall-through behavior.

• Ensure loop conditions eventually become false to avoid infinite loops.

• Keep nested blocks readable using proper indentation and structure.

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