java如何动态调用基类中由字符串值指定的子类方法？

Question

下面是一段代码

public class ChildB extends BaseA {
    public void showMessage() {
        Log.d("myTest", "Here is ChildB.");
    }
}


public class ChildC extends BaseA {
    public void showMessage() {
        Log.d("myTest", "Here is ChildC.");
    }
}


public class NormalD {
    public void showMessage() {
        Log.d("myTest", "Here is NormalD.");
    }
}


public class BaseA {
    public void showMessage(String sSpecifiedChild) {
        sSpecifiedChild.showMessage();  <== I'd like to invoke a child method specified by String value.
    }
}


public class MainActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_jelly_notification);

        BaseA baseA = new BaseA();

        baseA.showMessage("ChildC");
        baseA.showMessage("ChildB");
        baseA.showMessage("NormalD");   <== occurs an exception because "NormalD" is not child of BaseA.
    }
}

期望的结果是：
这是ChildC
这是ChildB

这是一个正常的例外