你可以告诉我，在创建a2对象后，为什么构造函数没有更改值

Question

有没有人可以告诉我，在创建a2对象后，为什么构造函数没有更改值？

public class HelloWorld 
{
    static int x;       // static datamembers
    static int y;       // static datamembers

    HelloWorld()        //constructor 
    {
        x = 9999;
        y = 9999;
    }

    static void display()      // static method
    {
        System.out.println("The value of x is:"+x);
        System.out.println("The value of y is:"+y);
    }

    void clear()
    {
        this.x = 0;      // this pointer
        this.y = 0;      // this pointer
    }

    public static void main(String []args) 
    {
        HelloWorld a1 = new HelloWorld();       // instance of class
        HelloWorld a2 = new HelloWorld();       // instance of class

        a1.display();       // a1 object calls the display
        a1.clear();         // this pointer clears the data
        a1.display();       // cleared data is displayed

        a2.display();       // a2 object calls the display but the values are 0 and 0 why not 9999 and 9999, why didn't the constructor get called?
    }
}

Answer 1

because of this line a1.clear(); your clear method is changing the orginal values of your static x, and y variables. Because if variable is static every object is referencing a single copy of original variable.