父類：
package test;
public class FatherClass {
protected int i=0;
}
子類：
package test;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class Child extends FatherClass {
public int i1=1;
public void function(){
System.out.println("call Child1 function");
}
public static void main(String []args) throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{
//開始執行main
System.out.println("the entrance.");
System.out.println("----------------");
//父類引用指向子類對象實例
FatherClass f;
f=new Child();
//f.function();//不符合語法規則，編譯不通過
System.out.println(f);
System.out.println(f.getClass());
System.out.println("----------------");
//子類引用指向子類對象實例
Child c1;
c1=(Child) f;
c1.function();
System.out.println(c1);
System.out.println(c1.getClass());
//運行時通過Method調用方法
Method m=Child.class.getMethod("function");
m.invoke(f);//輸出正常
//子類引用指向了父類實例，父類中並沒有void function()
//編譯正確但是運行錯誤
Child c2=(Child) new FatherClass();
m.invoke(c2);//Exception
/**
* Exception in thread "main" java.lang.ClassCastException:
* test.FatherClass cannot be cast to test.Child1
at test.Child1.main(Child1.java:36)
*/
}
}
輸出：
the entrance.
----------------
test.Child@2a139a55
class test.Child
----------------
call Child1 function
test.Child@2a139a55
class test.Child
call Child1 function
Exception in thread "main" java.lang.ClassCastException: test.FatherClass cannot be cast to test.Child
at test.Child.main(Child.java:37)
