How do I create static variables in Java?

By Wayan in Basic, Core API 0 Comment

Class variables or static variables are variables that are declared with static modifier. A given class will have only one copy of each of its static variables, regardless of how many times the class has been instantiated.

If the value of a static variable is changed, the new value is available equally in all instances of the class. The final keyword could be added to indicate the value of static variable will never change.

If you try to assign a new value to final variable, you will get a compile error.

package org.kodejava.basic;

public class StaticDemo {
    // static variable with final value that never change
    final static int Y = 20;
    // static variable
    static int x = 12;
    // non-static variable
    int z;

    public static void main(String[] args) {
        StaticDemo sd0 = new StaticDemo();

        System.out.println("x before update = " + StaticDemo.x);
        System.out.println("y= " + StaticDemo.Y);

        sd0.z = StaticDemo.x + StaticDemo.Y;
        System.out.println("z= " + sd0.z);

        StaticDemo.x = 15;
        System.out.println("x after update = " + StaticDemo.x);

        StaticDemo sd1 = new StaticDemo();
        StaticDemo sd2 = new StaticDemo();
        StaticDemo.x = 20;

        System.out.println("StaticDemo.x = " + StaticDemo.x);
        System.out.println("sd0 = " + sd0.getX());
        System.out.println("sd1 = " + sd1.getX());
        System.out.println("sd2 = " + sd2.getX());

        //
        // try to assign value to final variable, it will cause a
        // compile time error
        //
        // StaticDemo.Y = 30;
    }

    public int getX() {
        return StaticDemo.x;
    }
}

Here is the output printed by the program:

x before update = 12
y= 20
z= 32
x after update = 15
StaticDemo.x = 20
sd0 = 20
sd1 = 20
sd2 = 20
Wayan
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