um(Object obj) {
if (obj instanceof Point(int x, int y)) {
System.out.println(x+y);
}
}
Pattern Matching for switch （switch模式匹配） – JEP 441
switch 的模式匹配可以与Record Patterns结合使用 允许在任何对象上制定 switch 语句和表达式。看一下代码例子：
static String formatterPatternSwitch(Object obj) {
return switch (obj) {
case Integer i -> String.format("int %d", i);
case Long l -> String.format("long %d", l);
case Double d -> String.format("double %f", d);
case String s -> String.format("String %s", s);
case Position(int x, int y) -> String.format("String %s,String %s", x,y);
default -> obj.toString();
};
}
同时当编译器判断所有分支都已涵盖时，switch不再需要分支default，如下面的代码
void flyJava21(Direction direction) {
switch (direction) {
case CompassDirection.NORTH -> System.out.println("Flying north");
case CompassDirection.SOUTH -> System.out.println("Flying south");
case CompassDirection.EAST -> System.out.println("Flying east");
case CompassDirection.WEST -> System.out.println("Flying west");
case VerticalDirection.UP -> System.out.println("Gaining altitude");
case VerticalDirection.DOWN -> System.out.println("Losing altitude");
}
}
Generational ZGC（分代式 ZGC） -JEP 439
主要是增加了对分代的支持，提高垃圾回收的性能，看下整体描述
To ensure a smooth succession, we will initially make Generational ZGC available alongside non-generational ZGC. The -XX:+UseZGC command-line option will select non-generational ZGC; to select Generational ZGC, add the -XX:+ZGenerational option:
使用命令行选项 -XX:+UseZGC 将选择非分代式 ZGC；要选择分代式 ZGC，需要添加 -XX:+ZGenerational 选项。
$ java -XX:+UseZGC -XX:+ZGenerational ...
In a future release we intend to make Generational ZGC the default, at which point -XX:-ZGenerational w