說白了就是強(qiáng)制轉(zhuǎn)換,用父類的類型來操作子類的指針,因此調(diào)用范圍會(huì)限制在父類中,但是調(diào)用的是子類實(shí)現(xiàn)的方法

package?com.java.Obj;

public?class????Obj?{

????public??void?Test()
????{
????????System.out.println("Obj?Test");
????}
}

package?com.java.Obj;

public?class?Sub1?extends?Obj?{

????public??void?Test()
????{
????????System.out.println("Sub1?Test");
????}
}

package?com.java.Obj;

public?class?Sub2?extends?Obj?{

????public??void?Test()
????{
????????System.out.println("Sub2?Test");
????}
}

import?com.java.Obj.Obj;
import?com.java.Obj.Sub1;
import?com.java.Obj.Sub2;

public?class?Test11A?????{


?????public?void???check(Obj??j)?{
?????????j.Test();

????}

????public?static?void?main(String[]?args)?{
????????//?TODO?自動(dòng)生成的方法存根
????????Test11A?test11a?=?new?Test11A();
????????Obj?obj?=?new?Sub1();?
????????Obj?obj2?=?new?Sub2();??
????????test11a.check(obj);//調(diào)用子類的實(shí)現(xiàn)
????????test11a.check(obj2);//調(diào)用子類的實(shí)現(xiàn)

????????System.out.println("hello");

????}