003-支持并发的饿汉单例

public class HungrySingletion {
      // 静态初始化器, 由JVM来保证线程安全
      private final static HungrySingletion instance = new HungrySingletion();

      private HungrySingletion() {}

      public HungrySingletion getInstance() {

            return instance;
      }

}