In Java 17 (released only a few days ago), Pattern Matching for switch has been introduced as a preview language feature, which allows case labels with patterns rather than just constants. Here is an example showing how you can match on type patterns:
public static String typedPatternMatching(Object o) {
return switch(o) {
case null -> "I am null";
case String s -> "I am a String. My value is " + s;
case Integer i -> "I am an int. My value is " + i;
default -> "I am of an unknown type. My value is " + o.toString();
};
}
// Output:
> typedPatternMatching("HELLO")
"I am a String. My value is HELLO"
> typedPatternMatching(123)
"I am an int. My value is 123"
> typedPatternMatching(null)
"I am null"
> typedPatternMatching(0.5)
"I am of an unknown type. My value is 0.5"You can also use a guarded pattern in order to refine a pattern so that it is only matched on certain conditions, for example:
public static String guardedPattern(Collection<String> coll) {
return switch(coll) {
case List list && (list.size() > 10) ->
"I am a big List. My size is " + list.size();
case List list ->
"I am a small List. My size is " + list.size();
default ->
"Unsupported collection: " + coll.getClass();
};
}If you have a Sealed Class (made a permanent language feature in Java 17), the compiler can verify if the switch statement is complete so no default label is needed. For example:
sealed interface Vehicle permits Car, Truck, Motorcycle {}
final class Car implements Vehicle {}
final class Truck implements Vehicle {}
final class Motorcycle implements Vehicle {}
public static String sealedClass(Vehicle v) {
return switch(v) {
case Car c -> "I am a car";
case Truck t -> "I am a truck";
case Motorcycle m -> "I am a motorcycle";
};
}Published on Java Code Geeks with permission by Fahd Shariff, partner at our JCG program. See the original article here: Java 17: Pattern Matching for Switch Opinions expressed by Java Code Geeks contributors are their own. |
