package myPackage;

public class ChocolateBoiler {
    private boolean empty;
    private boolean boiled;
    private static ChocolateBoiler uniqueInstance;
    private ChocolateBoiler(){
        empty = true;
        boiled = false;
    }

    public static ChocolateBoiler getInstance(){
        if (uniqueInstance == null)
            uniqueInstance = new ChocolateBoiler();

        return uniqueInstance;
    }

    public boolean isEmpty(){
        return empty;
    }

    public boolean isBoiled(){
        return boiled;
    }

    public void fill(){
        if (isEmpty())
        {
            empty = false;
            boiled = false;
        }
    }

    public void drain(){
        if (!isEmpty() && isBoiled())
            empty = true;
    }

    public void boil(){
        if (!isEmpty() && !isBoiled())
            boiled = true;
    }
}


package myPackage;

public class Driver {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
ChocolateBoiler cb = ChocolateBoiler.getInstance();
cb.fill();
cb.drain();
System.out.println("cb mem address = " + cb.toString());

ChocolateBoiler cb2 = ChocolateBoiler.getInstance();
System.out.println("cb2 = " + cb.toString());
    }

}