package headfirst.singleton.chocolate; 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) {			System.out.println("Creating unique instance of Chocolate Boiler");			uniqueInstance = new ChocolateBoiler();		}		System.out.println("Returning instance of Chocolate Boiler");		return uniqueInstance;	}	public void fill() {		if (isEmpty()) {			empty = false;			boiled = false;			// fill the boiler with a milk/chocolate mixture		}	} 	public void drain() {		if (!isEmpty() && isBoiled()) {			// drain the boiled milk and chocolate			empty = true;		}	} 	public void boil() {		if (!isEmpty() && !isBoiled()) {			// bring the contents to a boil			boiled = true;		}	}  	public boolean isEmpty() {		return empty;	} 	public boolean isBoiled() {		return boiled;	}}