向上轉型Parent parent=new Son();

主要作用:引數統一

向下轉型(Son)parent.SonMethod();

主要作用:呼叫子類的特有方法

public class Parent {
    private static final String TAG = "Parent";
    public void ParentMethod(){
        Log.i(TAG, "ParentMethod: ");
    }
}

public class Son extends Parent {
    private static final String TAG = "Son";
    public void SonMethod(){
        Log.i(TAG, "SonMethod: ");
    }
}


Parent parent=new Son();
parent.ParentMethod();
((Son) parent).SonMethod();