SingleTone

/***
 * Single tone design pattern 
 * --------------------------
 * Ensure that a class has only one instance and 
 * provide a global point of access to it .
 * 
 */
public class SingleTone {

	public static SingleTone instance = null;
	
	private SingleTone(){
		System.out.println("Creating...");
	}
	
	public static SingleTone getInstance() {
		if(instance == null){
			instance = new SingleTone();
		}
		return instance;
	}

}

//and the main class
public class MainClass {
	public static void main(String[] args) {
		SingleTone singleTone1 = SingleTone.getInstance(); //you can not create instance by using new keyword because of private constructor 
		SingleTone singleTone2 = SingleTone.getInstance(); //you have to get it by calling getInstance method 
		
		print("singleTone1", singleTone1);
		print("singleTone2", singleTone2);
	}
	
	public static void print(String name, SingleTone tone) {
		System.out.println(String.format("Object : %s, Hashcode : %d", name,tone.hashCode()));
	}

}