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import java.util.List;
import java.util.Locale;
/**
* Inspired by examples in https://openjdk.org/jeps/427
*/
public class SwitchPatternPreview4OK {
public static void main(String[] args) {
System.out.println(formatterPatternSwitch(null));
System.out.println(formatterPatternSwitch(123));
System.out.println(formatterPatternSwitch(999L));
System.out.println(formatterPatternSwitch(12.34));
System.out.println(formatterPatternSwitch("foo"));
System.out.println(formatterPatternSwitch(List.of(123, "foo", 999L, 12.34)));
System.out.println(testCircle(new Rectangle()));
System.out.println(testCircle(new Circle(5)));
System.out.println(testCircle(new Circle(6)));
System.out.println(testSealedCoverage(new A()));
System.out.println(testSealedCoverage(new B()));
System.out.println(testSealedCoverage(new C(5)));
// 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 E<Integer>()));
}
static String formatterPatternSwitch(Object o) {
return switch (o) {
case null -> "null";
case Integer i -> String.format("int %d", i);
case Long l -> String.format("long %d", l);
case Double d -> String.format(Locale.ENGLISH, "double %f", d);
case String s -> String.format("String %s", s);
default -> o.toString();
};
}
static class Shape {}
static class Rectangle extends Shape {}
static class Circle extends Shape {
private final double radius;
public Circle(double radius) { this.radius = radius; }
double calculateArea() { return Math.PI * radius * radius; }
}
static String testCircle(Shape s) {
return switch (s) {
case Circle c when (c.calculateArea() > 100) -> "Large circle";
case Circle c -> "Small circle";
default -> "Non-circle";
};
}
sealed interface S permits A, B, C {}
final static class A implements S {}
final static class B implements S {}
static record C(int i) implements S {} // Implicitly final
static String testSealedCoverage(S s) {
return switch (s) {
case A a -> "Sealed sub-class A";
case B b -> "Sealed sub-class B";
case C c -> "Sealed sub-record C";
};
}
/**
* 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 5 with Java 21, Eclipse 4.28.
*/
/*
static String constantLabelMustAppearBeforePattern(Object o) {
switch (o) {
case null -> System.out.println("value unavailable: " + o);
case -1, 1 -> System.out.println("special case:" + o);
case Integer value when value > 0 -> System.out.println("positive integer: " + o);
case Integer i -> System.out.println("other integer: " + o);
default -> System.out.println("non-integer: " + o);
}
return o == null ? "null" : o.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 when 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 when value > 0 -> System.out.println("positive integer: " + i);
default -> System.out.println("other 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, 19 and 20.
*
* 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
*
* TODO: reactivate when implemented or move to preview 5 with Java 21.
*/
sealed interface I<T> permits D, E {}
final static class D<X> implements I<String> {}
final static class E<Y> implements I<Y> {}
static int testGenericSealedExhaustive(I<Integer> i) {
return switch (i) {
// Exhaustive as no D case possible!
case E<Integer> bi -> 42;
};
}
}
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