Java / Java 21 Coding Standards Interview Questions
How do you format a pattern-matching switch expression per Java 21 coding standards?
A pattern-matching switch is written as an expression using arrow syntax, with each case testing a type pattern rather than a constant, and the result assigned directly instead of through a mutable local variable.
String describe(Object obj) { return switch (obj) { case Integer i when i > 0 -> "positive integer"; case Integer i -> "non-positive integer"; case String s -> "string of length " + s.length(); case null -> "null value"; default -> "unknown"; }; }
Standards require pattern variables to be named descriptively rather than reused generic names like o, guard conditions introduced with when to stay short enough to read on one line, and a default branch present unless the type being switched on is sealed and every permitted subtype is already covered, in which case the compiler enforces exhaustiveness on its own.
In a pattern-matching switch expression, a guard condition is introduced with the keyword:
A default branch can safely be omitted from a switch over a type when:
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