单例模式的记录

1 class Single {
2     private Single(){};
3     private static final Single s = new Single();
4
5     public static Single getInstance(){
6         return s;
7     }
8 }

1 class Single {
2     private Single(){};
3     private static Single s = null;// 延迟加载
4
5     public static Single getInstance(){
6         if(null == s)//双重判断提高效率，后来的就不需要再判断锁内的内容，如果不符合条件就直接return
7             synchronized(Single.class)//同步代码块，该处的锁是这个类的字节码对象
8             {
9                 if(null ==s)
10                     s = new Single();
11             }
12         return s;
13     }
14 }