派生类如何调用基类的私有方法？

public class PrivateOverride {  

    private void f() {  
        System.out.println("private f()");  
    }
}  

public class Derived extends PrivateOverride {  

    public void f() {                         //this method is never run.
        System.out.println("public f()");     
    }  
}  

public static void main(String[] args) {

    // instantiate Derived and assign it to 
    // object po of type PrivateOverride.
    PrivateOverride po = new Derived();  

    // invoke method f of object po.  It
    // chooses to run the private method of PrivateOveride
    // instead of Derived
    po.f();                         
  }  
}  

因此，此代码的输出为 。现在，我脑海中浮现出一个问题：作为派生类对象的 po 如何调用作为其基类的 PrivateOverride 的私有方法？private f()