设计模式之单例模式

处理多线程----单例模式

1.当JVM加载到这个类的时候，马上创建一个实例

public class Singleton {
    private static Singleton uniqueInstance = new Singleton();

    private Singleton() {
    }

    public static Singleton getInstance() {
        return uniqueInstance;
    }
}

2.用"双重检查加锁"，在getInstance()减少使用同步 （仅支持Java 1.6）

public class Singleton {
    private volatile Singleton _instance;

    private Singleton() {

    }

    public Singleton getInstance() {
        if(_instance == null)
        {
            synchronized (Singleton.class) {
                if(_instance == null)
                    _instance = new Singleton();
            }
        }
        return _instance;
    }
}

不推荐方式

public synchronized Singleton getInstance() {
    if(_instance == null)
    {
        _instance = new Singleton();
    }
    return _instance;
}