public class SingletonDebug {
    private static SingletonDebug singletionDebug;
    private SingletonDebug(){

    }
    public static SingletonDebug getInstance(){
        if (singletionDebug == null){
            singletionDebug = new SingletonDebug();
        }
        return singletionDebug;
    }
}

public class T implements Runnable {
    @Override
    public void run() {
        SingletonDebug singletonDebug = SingletonDebug.getInstance();
        System.out.println(singletonDebug.hashCode());
    }
}

public class Main {
    public static void main(String[] args) {
        Thread t1 = new Thread(new T());
        Thread t2 = new Thread(new T());

        t1.start();
        t2.start();

        System.out.println("end of main");
    }
}