[设计模式] 单例设计模式

1.懒汉式（内部类式）

/**
 * Created by pmx on 14-9-14.
 */
public class Singleton {
    private Singleton() {}

    public static Singleton getInstance() {
        return SingletonHolder.instance;
    }

    static class SingletonHolder {
        private static Singleton instance = new Singleton();
    }
}

2.懒汉式（同步）

/**
 * Created by pmx on 14-9-14.
 */
public class Singleton {

    private static Singleton singleton = null;

    private Singleton() {}

    public static Singleton getInstance() {

        if (singleton == null)
        {
            synchronized (Singleton.class)
            {
                if (singleton == null)
                    singleton = new Singleton();
            }
        }
        return singleton;
    }

}