用 Java 解决一些我不确定的问题

Question

package Day4;

public class clasAndobjDemo {

    static int a = 90; //Data memeber ,Properties
    static int b = 100; // Data Memeber Poperties

    public static void main(String[] args) {
        clasAndobjDemo obj1 = new clasAndobjDemo();
        obj1.sub();
        obj1.sum();
        System.out.println(obj1.a);
        System.out.println(obj1.b);
        System.out.println(a);
        System.out.println(b);
    }

    public void sub() {
        int x = 80, y = 100, z = x - y;
        System.out.println("Print" + z);
    }

    public void sum() {
        int x = 80, y = 100, z = x + y;
        System.out.println("Print" + z);
    }
}

Output for above code is:

Print 20
Print 80
90
100
90
100

Can someone please help me to understand why I am getting:

90
100
90
100.

Answer 1

A static variable can be accessed in many ways.

Static variables can be accessed directly in both static/non-static method. Also, a static variable can be accessed from an object.

System.out.println(obj1.a);

However, the above method is discouraged.

Since static variables are owned by the class(only one copy for all the objects), you can access them without using instance references.

ie directly(within the class itself)

System.out.println(a);

or using classname

clasAndobjDemo.a

References : https://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html