关于动态绑定和静态绑定?

下面的代码，为什么第二个参数即便是Derived的对象调用的也是第二个参数是Base对象的方法?whichfoo实现的究竟是静态绑定还是动态绑定?

public class Test {
public static void main(String[] args) {
Base b=new Base();
Derived d=new Derived();

//测试传入不同参数时会调用哪个foo函数
whichFoo(b, b);//Base.Base
whichFoo(b, d);//Base.Base??
whichFoo(d, b);//Derived.Base
whichFoo(d, d);//Derived.Base??
}

public static void whichFoo(Base arg1,Base arg2){//static方法静态绑定???
arg1.foo(arg2);
}

class Base{
public void foo(Base x){
System.out.println("Base.Base");
}

public void foo(Derived x){
System.out.println("Base.Derived");
}
}

class Derived extends Base{
public void foo(Base x){
System.out.println("Derived.Base");
}

public void foo(Derived x){
System.out.println("Derived.Derived");
}
}
}