19) Static (and Final)

class Thing{

    //cannot change the value of "final" once has been initialized
    public final static int LUCKY_NUMBER = 7;

    public String name;
    public static String description;

    //because count is static, there is only one copy of count that exists in the class
    public static int count = 0;

    public int id;

    public Thing(){
        id = count;
        count ++;
    }

    public void showName(){
        System.out.println("Object id: " + id + ", " + description + ": " + name);
        Thing.showInfo();
    }

    //can only be accessed within the class, but cannot be accessed by the declared objects in the main class
    public static void showInfo(){
        System.out.println(description);
    }

}


public class Main {

    public static void main(String[] args) {

        //because String description is static in the class, it is associated with the class, not the objects that are instantiated
        //this works because the variable in the Thing class has been set to "public", if set to "private" this will not work
        Thing.description = "I am a thing";

        Thing.showInfo();

        System.out.println("Before creating objects, count is: " + Thing.count);

        Thing thing1 = new Thing();
        Thing thing2 = new Thing();

        System.out.println("After creating objects, count is: " + Thing.count);

        //each object gets its own name
        thing1.name = "Bob";
        thing2.name = "Sue";


        System.out.println(thing1.name);
        System.out.println(thing2.name);

        //Accessing the static value of PI in the Math class
        System.out.println(Math.PI);

        //Cannot change the constant value of PI
        //Math.PI = 15;

        System.out.println(Thing.LUCKY_NUMBER);

        thing1.showName();

    }
}