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package test;
class A {
    public String f(A obj)
    {
        return("A");
    }
}
class B extends A {
    public String f(B obj)
    {
        return("C");
    }
    public String f(A obj)
    {
        return("D");
    }
}
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B b = new B();
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A a;
a = b;
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ÄÇôϱߵÄÕâ¶Î²âÊÔ´úÂëµÄ´òÓ¡½á¹û¾ÍÊÇ“D”£¬ÒòΪa2Ö»ÄÜÓÐpublic String f(A obj) Õâ¸ö·½·¨ÊÇ¿ÉÒÔÓõġ£
public class TestObj
{
    public static void main(String args[])
    {  A a1 = new A();
        A a2 = new B(); //×ÓÀà¶ÔÏóת»¯Îª¸¸À࣬³ÆÎªÉÏתÐÍ£¬²»ÐèÒªÇ¿ÖÆ×ª»»¡£
        B b = new B();
        System.out.println(a2.f(b)); //“D”
        System.out.println();
         if (a2 instanceof B) {
             B b1 = (B) a2;  //¸¸Àà¶ÔÏóת»¯ÎªÏÂתÐÍ£¬´ËʱÐèҪʹÓÃÇ¿ÖÆ×ª»»£¬´ËʱÐèÒªÏÈÅжÏҪת»»µÄÕâ¸ö¶ÔÏó£¨Ò²¾ÍÊÇa2Ö¸ÏòµÄÕâ¸ö¶ÔÏó£©ÊDz»ÊÇBÀàµÄʵÀý
            System.out.println(b1.f(b));//"C"
      


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