Java: Switch Expression

Note: Not to be confused with switch statements.

Let's start with an example:

int i = switch (someString) {
    case "one" -> 1;
    case "two" -> 2;
    case "three" -> 3;
    default -> -1;
};

You can switch on integers, strings and enums.

Need to cover all cases

int i = 1;

// Compiles
// error: does not cover all possible input values
String str = switch (i) {
    case 1 -> "one";
    case 2 -> "two";
    case 3 -> "three";
    default -> "Something else";
}
 

Multiple case expressions

You can have multiple case expressions in one case line:

String str = switch (i) {
    case 1, 2, 3 -> "one, two, or three"
    default -> "Something else";
}

Blocks statements and break

You can use break to "return" values.

This allows for use of block statements.

String str = switch (i) {

    case 1 -> "one";

    case 2 -> break "two";

    case 3 -> {
        System.out.println("Third case!");
        break "three";
    }

    default -> "Something else";
};

Throw

Statements must be wrapped in { ... } except for a single throw statement.

int i = switch (someString) {
    case "one" -> 1;
    case "two" -> 2;
    case "three" -> 3;
    default -> throw new IllegalArgumentException();
};

Colon syntax

Colon syntax allows for statements even without { ... }.

Cases will fall through.

You must use break.

String str = switch (i) {

    case 1:
        System.out.println("One");
        System.out.println("Falling through!");

    case 2:
        break "Two";

    default:
        break "Something else";
};

You can not mix arrow and colon syntax in the same switch.

Enhanced Switch Statement

Switch expressions should not be confused with switch statements. (See Statements vs Expressions.)

The arrow syntax can be used in switch statements too, in which case fall through is disabled and break is disallowed.

See article Switch Statement.

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