原始类型模式匹配

  Object o = 42; if (o instanceof int i) println(i)
      JDK 21:编译失败 unexpected type
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:int 42
  int x = 300; if (x instanceof byte b) ...(int 能否精确转成 byte)
      JDK 21:编译失败 unexpected type
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:不能精确转成 byte
  int x = 100; if (x instanceof byte b) ...
      JDK 21:编译失败 unexpected type
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:byte 100
  long l = 5L; switch (l) { case 5L -> ... }(switch 长整型)
      JDK 21:编译失败 selector type long is not allowed
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:five
  boolean b = true; switch (b) { case true -> ... }
      JDK 21:编译失败 selector type boolean is not allowed
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:T
  double d = 1.5; switch (d) { case double x when x > 1 -> ... }
      JDK 21:编译失败 selector type double is not allowed
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:gt1
  Integer boxed = 7; switch (boxed) { case int i when i > 5 -> ... }
      JDK 21:编译失败 unexpected type
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:big
  int x = 3; switch (x) { case int i when i > 2 -> ... }
      JDK 21:编译失败 unexpected type
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:gt2

  float f = 16777217; int→float 精确吗
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:int 16777217 不能精确转成 float
  int x = 16777216; instanceof float
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:float 1.6777216E7
  long l = Integer.MAX_VALUE + 1L; instanceof int
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:long 超出 int 范围
  double d = 0.1; instanceof float
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:0.1 不能精确转成 float
  double d = 0.5; instanceof float
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:float 0.5
  char c = 65; int i = c; i instanceof char
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:char A
  int i = -1; instanceof char(范围外)
      JDK 27:编译失败 primitive patterns are a preview feature and are disabled by default.
      JDK 27+preview:-1 不是合法的 char

  JDK 21: javac 21.0.12.1
  JDK 27: javac 27
  JDK 27 不加 --enable-preview 编译 instanceof int: <jtmp>/j138m/T.java:1: error: primitive patterns are a preview feature and are disabled by default. ;  (use --enable-preview to enable primitive patterns)
  JDK 27 加 --enable-preview --release 27: 编译并运行:1