javaSE-单例设计模式的线程安全

//饿汉式class Single{private static final Single s = new Single();private Single(){}public static Single getInstance(){return s;}}class Single{private static Single s = null;private Single(){}public static synchronized Single getInstance(){if(s==null){if(s==null)s = new Single();}return s;}}//懒汉式/*加同步关键字，解决的是安全问题。加双重判断，是为了提高效率。*/class Single{private static Single s = null;private Single(){}public static  Single getInstance(){if(s==null){synchronized(Single.class){if(s==null){//-->0s = new Single();}}}return s;}}

以上代码全是是线程安全的  第三中既有效率 又有安全