多态的缺陷：域和静态方法

域和静态方法不具有多态性！！！（直接访问某个域，这个访问就将在编译器进行解析；）

//: polymorphism/FieldAccess.java

// Direct field access is determined at compile time.


class Super {
  public int field = 0;
  public int getField() { return field; }
}


class Sub extends Super {
  public int field = 1;
  public int getField() { return field; }
  public int getSuperField() { return super.field; }
}


public class FieldAccess {
  public static void main(String[] args) {
    Super sup = new Sub(); // Upcast
    System.out.println("sup.field = " + sup.field +
      ", sup.getField() = " + sup.getField());
    Sub sub = new Sub();
    System.out.println("sub.field = " +
      sub.field + ", sub.getField() = " +
      sub.getField() +
      ", sub.getSuperField() = " +
      sub.getSuperField());
  }
} /* Output:
sup.field = 0, sup.getField() = 1
sub.field = 1, sub.getField() = 1, sub.getSuperField() = 0

*///:~

//: polymorphism/StaticPolymorphism.java
// Static methods are not polymorphic.


class StaticSuper {
  public static String staticGet() {
    return "Base staticGet()";
  }
  public String dynamicGet() {
    return "Base dynamicGet()";
  }
}


class StaticSub extends StaticSuper {
  public static String staticGet() {
    return "Derived staticGet()";
  }
  public String dynamicGet() {
    return "Derived dynamicGet()";
  }
}


public class StaticPolymorphism {
  public static void main(String[] args) {
    StaticSuper sup = new StaticSub(); // Upcast
    System.out.println(sup.staticGet());
    System.out.println(sup.dynamicGet());
  }
} /* Output:
Base staticGet()
Derived dynamicGet()
*///:~