单例模式-懒汉式-双重检查锁实现

public class SingletonTest {
    private static volatile SingletonTest singletonTest;
    public static SingletonTest getInstance(){
        if(singletonTest == null){
            synchronized (SingletonTest.class) {
                if (singletonTest == null) {
                    singletonTest = new SingletonTest();
                }
            }
        }
        return singletonTest;
    }
}

妙啊