在Java开发的世界里，有一个几乎所有程序员都深恶痛绝却又屡屡中招的“幽灵错误”——空指针异常（NullPointerException，简称NPE）。它像一颗隐藏在代码深处的定时炸弹，可能在你最不经意的时刻突然爆发：当你调用一个未初始化对象的方法时，当你在集合中遍历一个null元素时，甚至当你以为某个返回值“肯定不为null”却事与愿违时，程序便会抛出那句经典的java，lang，NullPoi ...

It doesn’t take much Java development experience to learn firsthand what the NullPointerException is about. In fact, one person has highlighted dealing with this as the number one mistake Java ...