Singleton单例

//多线程-非单例
public class Singleton {
    private static Singleton INSTANCE;
    public static Singleton getInstance() {
        if (isNull(INSTANCE)) {
            try {
                Thread.sleep(1);
                INSTANCE = new Singleton();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        return INSTANCE;
    }
    public static void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            new Thread(() -> System.out.println(Singleton.getInstance().hashCode())).start();
        }
    }
}