Guarded patterns with when

Code Comparison

if (shape instanceof Circle) {
    Circle c = (Circle) shape;
    if (c.radius() > 10) {
        return "large circle";
    } else {
        return "small circle";
    }
} else {
    return "not a circle";
}

return switch (shape) {
    case Circle c
        when c.radius() > 10
            -> "large circle";
    case Circle c
            -> "small circle";
    default -> "not a circle";
};

Why the modern way wins

🎯

Precise matching

Combine type + condition in a single case label.

📐

Flat structure

No nested if/else inside switch cases.

📖

Readable intent

The when clause reads like natural language.

Modern Approach

when Clause

JDK Support

Guarded patterns with when

Available

Widely available since JDK 21 LTS (Sept 2023)

How it works

Guarded patterns let you refine a type match with an additional boolean condition. This keeps all the branching logic in the switch instead of nesting if statements inside cases.