Singleton Class

class CoffeeMachine {
    private float coffeeQty;
    private float milkQty;
    private float waterQty;
    private float sugarQty;

    static private CoffeeMachine instance = null; // static, since it's accessed by the static getInstance() method below

    private CoffeeMachine() { // private constructor, so you can't create an object of CoffeeMachine directly
        coffeeQty = 1;
        milkQty = 1;
        waterQty = 1;
        sugarQty = 1;
    }

    public void fillWater(float qty) {
        waterQty = qty;
    }
    public void fillSugar(float qty) {
        sugarQty = qty;
    }
    public float getCoffee() {
        return 0.23f;
    }

    static public CoffeeMachine getInstance() { // creates (once) and returns the single instance
        if (instance == null) {
            instance = new CoffeeMachine();
        }
        return instance;
    }
}

public class Singleton {
    public static void main(String[] args) {
        CoffeeMachine m1 = CoffeeMachine.getInstance();
        CoffeeMachine m2 = CoffeeMachine.getInstance();
        CoffeeMachine m3 = CoffeeMachine.getInstance();

        System.out.println(m1 + " " + m2 + " " + m3);
        if (m1 == m2 && m1 == m3) {
            System.out.println("Same");
        }
    }
}