说明：  异常指的是程序运行时出现的非正常情况，又称为差错、违例等。在上一节中介绍的运行错误就是异常的主要现象。当异常现象发生时，会造成程序运行中断、系统死机等问题。Java程序可以用特定语句来处理异常并继续程序执行，而不让程序中断。Java语言提供一个异常处理类Exception类，专门处理程序执行期间的错误。每当Java程序运行过程中发生一个可识别的运行错误时，即该错误有一个异常类与之相对应时，系统都会产生一个相应的该异常类的对象，即产生一个异常。Java语言异常处理机制有以下一些优点
(Abnormal refers to the program running when the abnormal situation of, also known as discrepancies, violations, etc. In the previous section of the mistake is abnormal operation introduced the main phenomenon. When abnormal phenomenon occurs, can cause to run the program interrupt, system crash. Java program can use specific statements to deal with problems and continue program execution, and don t let the interruption of the program. Java language provides a Exception handling class Exception classes, special processing program during the execution of mistakes. Whenever Java program running occurred in the process of identification of a runtime error, the wrong when there is an exception class and the relative, the system will generate a timely corresponding the abnormal objects of a class, which produce an exception. Java language exception handling mechanism has the following some advantages )