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🏷 Switch Expressions 6 patterns

Topic: Switch Expressions

All Java patterns related to Switch Expressions — java.evolved

Switch expressions

Old String msg; switch (day) { case MONDAY: msg = "Start"; break; case FRIDAY: msg = "End"; break; default: msg = "Mid"; }

Modern String msg = switch (day) { case MONDAY -> "Start"; case FRIDAY -> "End"; default -> "Mid"; };

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JDK 14+ learn more →

Pattern matching in switch

Old String format(Object obj) { if (obj instanceof Integer i) return "int: " + i; else if (obj instanceof Double d) return "double: " + d; else if (obj instanceof String s) return "str: " + s; return "unknown"; }

Modern String format(Object obj) { return switch (obj) { case Integer i -> "int: " + i; case Double d -> "double: " + d; case String s -> "str: " + s; default -> "unknown"; }; }

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JDK 21+ learn more →

Guarded patterns with when

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

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

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JDK 21+ learn more →

Primitive types in patterns

Old String classify(int code) { if (code >= 200 && code < 300) return "success"; else if (code >= 400 && code < 500) return "client error"; else return "other"; }

Modern String classify(int code) { return switch (code) { case int c when c >= 200 && c < 300 -> "success"; case int c when c >= 400 && c < 500 -> "client error"; default -> "other"; }; }

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JDK 25+ learn more →

Exhaustive switch without default

Old // Must add default even though // all cases are covered double area(Shape s) { if (s instanceof Circle c) return Math.PI * c.r() * c.r(); else if (s instanceof Rect r) return r.w() * r.h(); else throw new IAE(); }

Modern // sealed Shape permits Circle, Rect double area(Shape s) { return switch (s) { case Circle c -> Math.PI * c.r() * c.r(); case Rect r -> r.w() * r.h(); }; // no default needed! }

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JDK 21+ learn more →

Null case in switch

Old // Must check before switch if (status == null) { return "unknown"; } return switch (status) { case ACTIVE -> "active"; case PAUSED -> "paused"; default -> "other"; };

Modern return switch (status) { case null -> "unknown"; case ACTIVE -> "active"; case PAUSED -> "paused"; default -> "other"; };

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JDK 21+ learn more →