Android_单例模式

使一个类只在内存中实例化一次

public class Singleton {      private static volatile Singleton instance;        private Singleton() {        }        public static Singleton getInstance() {          if (instance == null) {              synchronized (Singleton.class) {                  if (instance == null) {                      instance = new Singleton();                  }              }          }          return instance;      }  }