🧑🏫 Java 21 Pattern Matching with switch and when Clauses

In Java, you can combine pattern matching in switch statements with guards,

which are additional when clauses used to refine the conditions for a match. This is known as a guarded pattern label.

A guard is simply a Boolean expression that must evaluate to true for the case to apply, after the pattern itself has matched.

🎩 Classic Approach (Pre-Pattern Matching)

Let’s say we’re modeling performers in a Parisian cabaret. We want to treat performers with short stage names differently.

💃 Modern Approach with when Clause

With pattern matching and when, we can make this more elegant and expressive:

🪄 What's Happening Behind the Curtain?

🟣 case String name when name.length() == 1

This matches if the performer is a String and the name has exactly one character – perhaps a mysterious cabaret star named “Z”.

🟣 case String name

This catches any other performer names that are still String, but longer than one character.

🟣 default

Handles anything that’s not a String – perhaps an object representing a light technician or a sound engineer.

🎭 Syntax Breakdown: p when e

A guarded pattern label follows this format:

🟣 The pattern (p) declares variables you can use inside the guard expression (e).

🟣 The guard (when) checks an additional condition.

🟣 If both the pattern and the guard match, the corresponding block executes.

📝 Final Thoughts

Using when clauses in switch makes your logic:

🟣 More concise

🟣 Easier to read

🟣 And way more expressive, just like a night at the Moulin Rouge 🌹