if, else and switch

Decision-making is in almost every method, and modern switch removes a whole class of fall-through bugs.

An if statement runs a block when a boolean condition is true, with optional else if and else branches. Always use braces, even for one line — it prevents bugs when someone adds a second statement later.

When you branch on one value against several constants, use switch. Modern Java (14+) has the arrow form, which does not fall through and can be used as an expression that yields a value:

String type = switch (day) {
    case SATURDAY, SUNDAY -> "weekend";
    default -> "weekday";
};

Several labels can share one case, separated by commas.
A switch expression must be exhaustive: every possible input needs a case, usually via default. For enums the compiler accepts listing every constant instead.
If a case needs several statements, use a block and yield the result: case 3 -> { log(); yield "three"; }.

You can switch on int, char, String, enums and (since Java 21) any type with pattern-matching cases, which you'll meet later.

The old colon form case 1: still works but falls through into the next case unless you write break. Forgetting break is a classic bug, so prefer arrows in new code.

For simple two-way choices that produce a value, the ternary cond ? a : b is often clearest. For complex conditions, extract them into a well-named boolean variable or method so the if reads like a sentence.

Example

public class Grades {
    static String letter(int score) {
        if (score >= 90) {
            return "A";
        } else if (score >= 75) {
            return "B";
        } else {
            return "C";
        }
    }

    public static void main(String[] args) {
        String cmd = "stop";
        int code = switch (cmd) {
            case "start", "run" -> 1;
            case "stop" -> {
                System.out.println("stopping...");
                yield 0;
            }
            default -> -1;
        };
        System.out.println(letter(82) + " " + code); // B 0
    }
}

Remember

Arrow-form switch never falls through and can return a value
Switch expressions must be exhaustive — add default (or cover every enum constant)
Use yield to return a value from a multi-statement case block

Watch out for

Using old case X: labels and forgetting break, so execution falls into the next case.

Check yourself

What does this print? `int n = 2; String s = switch (n) { case 1 -> "one"; case 2 -> "two"; default -> "many"; }; System.out.println(s);`

Official docs: docs.oracle.com/en/java/javase/21/language/switch-expressions-and-statements.html

Example

Remember

Watch out for

Check yourself

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