Polymorphism and Static Methods

问题

I have a question about this code right here

public Car {
    public static void m1(){
        System.out.println("a");
    }
    public void m2(){
        System.out.println("b");
    }
}

class Mini extends Car {
    public static void m1() {
        System.out.println("c");
    }
    public void m2(){
        System.out.println("d");
    }
    public static void main(String args[]) {
        Car c = new Mini();
        c.m1();
        c.m2();       
   }
}

I know that polymorphism does not work with static methods, only to instance methods. And also that overriding doesn't work for static methods.

Therefore I think that this program should print out: c, d

Because c calls the m1 method, but it's static, so it can't override and it calls the method in class Mini instead of Car.

Is this correct?

However, my textbook says that the answer should be : a, d

is it a typo? Because I'm a little confused right now.

Please clear this up, thanks.

回答1:

Because c calls the m1 method, but it's static, so it can't override and it calls the method in class Mini instead of Car.

That's exactly backwards.

c is declared as Car, so static method calls made through c will call methods defined by Car.
The compiler compiles c.m1() directly to Car.m1(), without being aware that c actually holds a Mini.

This is why you should never call static methods through instance like that.

来源：https://stackoverflow.com/questions/13695999/polymorphism-and-static-methods