public class MyBenchmark {
	public static void main(String[] args) {
		new Thread(()-> {
			Singleton instance1 = Singleton.getInstance();
		},"t1").start();
		
		new Thread(()-> {
			Singleton instance2 = Singleton.getInstance();
		},"t2").start();
	}
}
@Slf4j(topic = "c.Singleton"
 
)
class Singleton {
	private static Singleton instance;
	private Singleton() {}
	public static Singleton getInstance() {
		if(instance == null) {
			instance = new Singleton();
			log.debug("已建立");  //若是單執行緒，則永遠只會輸出1次。多執行緒，則可能會輸出多次
		}
		return instance;
	}
}