Sealed Class 与反射:运行时如何看到允许的子类型

  Shape.isSealed() = true,isInterface = true,修饰符 = public abstract interface
  Shape.getPermittedSubclasses() = [Circle, Square, Poly]
    Circle  isSealed=false final=true  record=true  修饰符=public final
    Square  isSealed=false final=true  record=false 修饰符=public final
    Poly    isSealed=false final=false record=false 修饰符=public
  非 sealed 类 Poly.getPermittedSubclasses() = null(null 表示不是 sealed);Tri 继承 non-sealed 的 Poly,Tri.isSealed() = false
  Shape.class.getPermittedSubclasses() 的顺序与源码 permits 的顺序:[Circle, Square, Poly](源码是 Circle, Square, Poly)

  javap -v shapes.Shape 里的属性:
    PermittedSubclasses
    #8 = Class              #9             // shapes/Circle
    #9 = Utf8               shapes/Circle
    #10 = Class              #11            // shapes/Square
    #11 = Utf8               shapes/Square
  Circle 的 class 文件里有 PermittedSubclasses 吗: False ;Poly(non-sealed)里有吗: False

  javac:不在 permits 里的 Extra implements Shape → ["<jtmp>/j84b/shapes/Extra.java:1: error: class is not allowed to extend sealed class: Shape (as it is not listed in its 'permits' clause)"]
  javac:允许的子类 Square 没有写 final / sealed / non-sealed → ['<jtmp>/j84c/shapes/Square.java:1: error: sealed, non-sealed or final modifiers expected']
  运行时:Extra.class 声明继承 Shape,但新的 Shape.class 的 permits 里没有它 → IncompatibleClassChangeError: class shapes.Extra cannot implement sealed interface shapes.Shape

  circle square poly
  旧的 App.class 遇到新子类 Hexagon → java.lang.MatchException: null
  App.name 的字节码里有 MatchException: True ;invokedynamic typeSwitch: True