Decision Making: if, else if, switch

if and else

int marks = 72;

if (marks >= 90) {
    System.out.println("Grade A");
} else if (marks >= 70) {
    System.out.println("Grade B");
} else {
    System.out.println("Keep practising!");
}

The condition inside the parentheses must produce a boolean. If it is true the block runs, otherwise control moves to the next else if or else.

Nested if

int age = 19;
boolean hasId = true;

if (age >= 18) {
    if (hasId) {
        System.out.println("Entry allowed");
    } else {
        System.out.println("ID required");
    }
}

switch Statement

int day = 3;
switch (day) {
    case 1: System.out.println("Monday"); break;
    case 2: System.out.println("Tuesday"); break;
    case 3: System.out.println("Wednesday"); break;
    default: System.out.println("Another day");
}

The break stops the switch from falling through to the next case. Java 14 added the arrow form which removes the need for break:

switch (day) {
    case 1 -> System.out.println("Monday");
    case 2 -> System.out.println("Tuesday");
    default -> System.out.println("Another day");
}

When to Use Which

• Use if/else for ranges (e.g. scores 70-89) and complex conditions.
• Use switch for exact equality against a fixed set of values.

Key Points

• Conditions must be boolean expressions.
• Always break (or use arrow syntax) to avoid fall-through.
• default handles every unlisted value.