public class Main {

public static void main(String[] args) {
    Singleton s1 = Singleton.getInstance();
    Singleton s2 = Singleton.getInstance();
    System.out.println(s1 == s2);
}

}

class Singleton {

private static Singleton instance;

private Singleton() {

}

//write your code here......单例模式有5种实现方式
public static Singleton getInstance(){
    if(instance == null){
        instance = new Singleton();
    }
    return instance;
}

}