要保证在多线程环境下的单例模式，有下面两种建议的方式：

一、静态内部类

public class Singletion {        private static class InnerSingletion {        private static Singletion single = new Singletion();    }        public static Singletion getInstance(){        return InnerSingletion.single;    }    }

 

 二、double check的方式

public class DubbleSingleton {    private static DubbleSingleton ds;        public  static DubbleSingleton getDs(){        if(ds == null){            try {                //模拟初始化对象的准备时间...                Thread.sleep(3000);            } catch (InterruptedException e) {                e.printStackTrace();            }            synchronized (DubbleSingleton.class) {                if(ds == null){                    ds = new DubbleSingleton();                }            }        }        return ds;    }        public static void main(String[] args) {        Thread t1 = new Thread(new Runnable() {            @Override            public void run() {                System.out.println(DubbleSingleton.getDs().hashCode());            }        },"t1");        Thread t2 = new Thread(new Runnable() {            @Override            public void run() {                System.out.println(DubbleSingleton.getDs().hashCode());            }        },"t2");        Thread t3 = new Thread(new Runnable() {            @Override            public void run() {                System.out.println(DubbleSingleton.getDs().hashCode());            }        },"t3");                t1.start();        t2.start();        t3.start();    }    }