java - ClassCastException 冒险

Question

我有 -

class A {
    // contains certain set() and get() methods
}

class B extends A {
    public A getAotherMethod() {
      A a = new A();
      // Contains some logic
      return a
      }
}

class C extends B {
    // contains certain set() and get() methods
}

class D {
    public Object getMethod() {

      B b = new B();
      // Contains some logic
      return b.getAnotherMethod()
     }
}


public static void main(String[] args) {
    A a = new A();
    B b = new B();
    C c = new C();
    D d = new D();
    c = (C) d.getMethod(); // This is giving me ClassCastException
}

Answer 1

d.getMethod();

这将在内部调用b.getAnotherMethod()，其中有

A a = new A();
// Contains some logic
return a

A 类的对象无法转换为C 类

我们可以将子类对象分配给父类(super class)引用，但我们不能将父类(super class)对象分配给子类引用，什么是在这种情况下由您完成。