为什么我们不能在扩展类的静态方法中使用此实例？

Question

Base class

class Basics415 {   

    Basics1 b1 = new Basics1();

    public static void main_hooo(){
        out.println("1234");     
    }

    void main_ho(){

    }

}

Extended class

public class Basics5 extends Basics415{     

    public static void main(String[] args){

        this.main_hooo();  // this line throws error.
    }

}

Why we aren't able to use this instance inside a static method of the extended class?

Answer 1

Your main method is static, which means there is no instance of Basic associated with it so this won't work. To access the static methods of Basics415 , you should refer to them explicitly like this:

public class Basics5 extends Basics415{
    public static void main(){
        Basics415.main_hooo();
    }
}

You could also just do this since Basic5 extends Basic415 . Both are acceptable, but your org may have their own style guidelines:

public class Basics5 extends Basics415{
    public static void main(){
        main_hooo();
    }
}

Answer 2

That is not the correct way to access a static method. this is not static. Instead do Basic5.main_hooo()

Answer 3

this和static彼此相反，就这么简单。如果要使用它，请在非静态方法中使用它。

Answer 4

The main() method must be defined with a String[] parameter if you want it to execute first. Also, main() is a static method (it belongs to the class). There is no instance (this) to refer to.

Use the class name to call it within main:

Basics415.main_hooo();  // this line no longer throws an error.

Answer 5

For static method not require create an object,

    public static void main(String[] args) {
        Basics415 b = new Basics415();
        b.main_hooo();// output : 1234
        main_hooo();// output : 1234
        Basics415.main_hooo();// output : 1234
    }