public class Singleton{
	private static Singleton singleton = new Singleton();
	private Singleton(){
		System.out.println("only one");
	}
	public static Singleton getInstance(){
		return singleton;	
	}
}

public class Main {
	public static void main(String[] args){
		Singleton instance1 = Singleton.getInstance();
		Singleton instance2 = Singleton.getInstance();

		System.out.println(instaince1 == instance2); //true
	}
}