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/**
* Inspired by examples in https://openjdk.java.net/jeps/420
*/
public class SwitchPatternPreview2OK {
public static void main(String[] args) {
// constantLabelMustAppearBeforePattern(-1);
// constantLabelMustAppearBeforePattern(0);
// constantLabelMustAppearBeforePattern(42);
// constantLabelMustAppearBeforePattern(-99);
// constantLabelMustAppearBeforePattern(Integer.valueOf(123));
// constantLabelMustAppearBeforePattern(null);
constantLabelMustAppearBeforePatternInteger(-1);
constantLabelMustAppearBeforePatternInteger(0);
constantLabelMustAppearBeforePatternInteger(42);
constantLabelMustAppearBeforePatternInteger(-99);
constantLabelMustAppearBeforePatternInteger(Integer.valueOf(123));
constantLabelMustAppearBeforePatternInteger(null);
// System.out.println(testGenericSealedExhaustive(new B<Integer>()));
}
/**
* According to an example from JEP 420, this should work, but it does not, neither with Javac nor ECJ.
*
* See:
* https://openjdk.java.net/jeps/420#1b--Dominance-of-pattern-labels
* https://bugs.openjdk.java.net/browse/JDK-8273326
* https://bugs.eclipse.org/bugs/show_bug.cgi?id=579355
*
* TODO: reactivate when implemented or move to preview 3 with Java 19, Eclipse 4.24.
*/
/*
static String constantLabelMustAppearBeforePattern(Object o) {
switch (o) {
case null -> System.out.println("value unavailable: " + i);
case -1, 1 -> System.out.println("special case:" + o);
case Integer i && i > 0 -> System.out.println("positive integer: " + o);
case Integer i -> System.out.println("other integer: " + o);
default -> System.out.println("non-integer: " + o);
}
return i == null ? "null" : i.toString();
}
*/
static String constantLabelMustAppearBeforePatternInteger(Integer i) {
switch (i) {
case null -> System.out.println("value unavailable: " + i);
case -1, 1 -> System.out.println("absolute value 1: " + i);
case Integer value && value > 0 -> System.out.println("positive integer: " + i);
default -> System.out.println("other integer: " + i);
}
return i == null ? "null" : i.toString();
}
static void nullCanAppearAfterConstantLabel(Integer i) {
switch (i) {
case -1, 1 -> System.out.println("absolute value 1: " + i);
case null -> System.out.println("value unavailable: " + i);
case Integer value && value > 0 -> System.out.println("positive integer: " + i);
default -> System.out.println("other integer: " + i);
}
}
static void defaultCanAppearBeforePattern(Integer i) {
switch (i) {
case null -> System.out.println("value unavailable: " + i);
case -1, 1 -> System.out.println("absolute value 1: " + i);
default -> System.out.println("other integer: " + i);
case Integer value && value > 0 -> System.out.println("positive integer: " + i);
}
}
static void defaultCanAppearBeforeNull(Integer i) {
switch (i) {
case -1, 1 -> System.out.println("absolute value 1: " + i);
default -> System.out.println("other integer: " + i);
case null -> System.out.println("value unavailable: " + i);
case Integer value && value > 0 -> System.out.println("positive integer: " + i);
}
}
static void defaultCanAppearBeforeConstantLabel(Integer i) {
switch (i) {
case null -> System.out.println("value unavailable: " + i);
default -> System.out.println("other integer: " + i);
case -1, 1 -> System.out.println("absolute value 1: " + i);
case Integer value && value > 0 -> System.out.println("positive integer: " + i);
}
}
/**
* According to an example from JEP 420, this should work with preview 2 (Java 18), and it does with Javac,
* but not with ECJ for Java 18 and 19.
*
* See:
* https://openjdk.java.net/jeps/420#2--Exhaustiveness-of-switch-expressions-and-statements
* https://bugs.eclipse.org/bugs/show_bug.cgi?id=579360
* https://github.com/eclipse-jdt/eclipse.jdt.core/issues/587
*/
/*
sealed interface I<T> permits A, B {}
final static class A<X> implements I<String> {}
final static class B<Y> implements I<Y> {}
static int testGenericSealedExhaustive(I<Integer> i) {
return switch (i) {
// Exhaustive as no A case possible!
case B<Integer> bi -> 42;
};
}
*/
}
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