Java适用于高并发的单例模式

    将synchronized放在 if ( mInstance == null ) 而不直接添加在getInstance方法上，是避免每次都同步该方法而导致的效率低下，当mInstance初始化过后则不需要同步。保证了效率。简单实现如下： 

package com.umeng.dp.singleton;

/**
 * @Copyright: Umeng.com, Ltd. Copyright 2011-2015, All rights reserved
 * @Title: ThreadSingleton.java
 * @Package com.umeng.dp.singleton
 * @Description: 线程安全的单例模式, synchronized放在mInstance == null条件中保证高并发。
 * @author Honghui He
 * @version V1.0
 */

public class ThreadSingleton {

    private static volatile ThreadSingleton mInstance = null;

    /**
     * @Title: ThreadSingleton
     * @Description: ThreadSingleton Constructor
     */
    private ThreadSingleton() {
    }

    /**
     * @Title: getInstance
     * @Description: 获取实例
     * @return 返回单例
     * @throws
     */
    public static ThreadSingleton getInstance() {
        if (mInstance == null) {
            synchronized (ThreadSingleton.class) {
                if ( mInstance == null ) {
                     mInstance = new ThreadSingleton();   }
            }
        }
        return mInstance;
    }

}