多态性和静态方法 [英] Polymorphism and Static Methods

问题描述

我对此代码有疑问

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();       
   }
}

我知道多态不适用于静态方法，仅限实例方法。而且覆盖对静态方法也不起作用。

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

因此我认为这个程序应该打印出来：c，d

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

因为c调用了m1方法，但它是静态的，所以它不能覆盖它并且它在类Mini而不是Car中调用方法。

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.

是这是正确的吗？

然而，我的教科书说答案应该是：a，d

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

是不是错字？因为我现在有点困惑。

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

请清除它，谢谢。

推荐答案

因为c调用m1方法，但它是静态的，所以它不能覆盖和它在类Mini中调用方法而不是Car。

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.

这完全是倒退。

c 声明为 Car ，因此通过<$进行静态方法调用c $ c> c 将调用 Car 定义的方法。

编译器编译 c。 m1（）直接到 Car.m1（），实际上并没有意识到 c 持有 Mini 。

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.

这就是你永远不应该通过像这样的实例调用静态方法的原因。

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

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