Mikel
[转载]Java 创建用户异常类、将异常一直向上抛、 throw和throws的区别 – 高杰才_Android – 博客园.
如果java提供的系统异常类型不能满足程序设计的需求，那么可以设计自己的异常类型。
从java异常类的结构层次可以看出，java类型的公共父类为Throwable.在程序运行中可能出现俩种问题：一种是由硬件系统或JVM导致 的故障，java定义该故障为Error,这类问题是用户程序不能够处理的；另外一种问题是程序运行错误，java定义为Exception，这种情况 下，可以通过程序设计调整来实现异常处理。
因此，用户定义的异常类型必须是Throwable的直接或间接子类。我推荐大家的异常类型以Exception为直接父类。下面开始我们的自定义异常类之旅…
1、首先定义自己的异常类AgeOutOfBound
<span class="com">/*** 自定义异常类* */</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">AgeOutOfBound</span><span class="pln"> </span><span class="kwd">extends</span><span class="pln"> </span><span class="typ">Exception</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="typ">AgeOutOfBound</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"Sorry,age out of bound !"</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span> |
2、定义一个类，根据参数值判断是否抛出异常
<span class="com">/*** 定义一个方法，根据参数值决定是否抛出异常* */</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">AgeInput</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> checkAage</span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> age</span><span class="pun">)</span><span class="kwd">throws</span><span class="pln"> </span><span class="typ">AgeOutOfBound</span><span class="pun">{</span><span class="pln"> </span><span class="com">//用关键字throws指明调用此方法可能抛出的异常</span><span class="pln"></span><span class="kwd">if</span><span class="pun">(</span><span class="pln">age</span><span class="pun">&</span><span class="pln">gt</span><span class="pun">;</span><span class="lit">0</span><span class="pln"> </span><span class="pun">&</span><span class="pln">amp</span><span class="pun">;&</span><span class="pln">amp</span><span class="pun">;</span><span class="pln"> age</span><span class="pun">&</span><span class="pln">lt</span><span class="pun">;</span><span class="lit">200</span><span class="pun">){</span><span class="pln"></span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"right!"</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="kwd">else</span><span class="pun">{</span><span class="pln"></span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"---------------"</span><span class="pun">);</span><span class="pln"></span><span class="kwd">throw</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">AgeOutOfBound</span><span class="pun">();</span><span class="pln"> </span><span class="com">//抛出异常用关键字throw</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span> |
3、
<span class="com">/*** 测试类，如果有异常场则捕获* */</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Demo</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> main</span><span class="pun">(</span><span class="typ">String</span><span class="pun">[]</span><span class="pln"> args</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">int</span><span class="pln"> age </span><span class="pun">=</span><span class="pln"> </span><span class="lit">100</span><span class="pun">;</span><span class="pln"></span><span class="kwd">try</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="typ">AgeInput</span><span class="pun">.</span><span class="pln">checkAage</span><span class="pun">(</span><span class="pln">age</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"> </span><span class="kwd">catch</span><span class="pln"> </span><span class="pun">(</span><span class="typ">AgeOutOfBound</span><span class="pln"> e</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Are you rellly :"</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> age </span><span class="pun">+</span><span class="pln"> </span><span class="str">" years old?"</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span> |
运行结果:当age=100,输入right
当age = 300,输出
—————
Sorry,age out of bound !Are you rellly :300 years old?
如有哪里不懂，可以到这里下载项目代码
http://download.csdn.net/detail/gaojiecaiandroid/6525621
补充：
下面说说throw和throws的区别
throws关键字通常被应用在声明方法时，用来指定可能抛出的异常。多个异常可以使用逗号隔开。当在主函数中调用该方法时，如果发生异常，就会将异常抛给指定异常对象。如下面例子所示：
<span class="kwd">public</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Shoot</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="pun">创建类</span><span class="pln"></span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> pop</span><span class="pun">()</span><span class="pln"> </span><span class="kwd">throws</span><span class="pln"> </span><span class="typ">NegativeArraySizeException</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="com">//定义方法并抛出NegativeArraySizeException异常</span><span class="pln"></span><span class="kwd">int</span><span class="pln"> </span><span class="pun">[]</span><span class="pln"> arr </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="kwd">int</span><span class="pun">[-</span><span class="lit">3</span><span class="pun">];</span><span class="com">//创建数组</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> main</span><span class="pun">(</span><span class="typ">String</span><span class="pun">[]</span><span class="pln"> args</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="com">//主方法</span><span class="pln"></span><span class="kwd">try</span><span class="pln"> </span><span class="pun">{</span><span class="pln">pop</span><span class="pun">();</span><span class="pln"> </span><span class="com">//调用pop()方法</span><span class="pln"></span><span class="pun">}</span><span class="pln"> </span><span class="kwd">catch</span><span class="pln"> </span><span class="pun">(</span><span class="typ">NegativeArraySizeException</span><span class="pln"> e</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"pop()方法抛出的异常"</span><span class="pun">);</span><span class="com">//输出异常信息</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span> |
2、throw关键字通常用在方法体中，并且抛出一个异常对象。程序在执行到throw语句时立即停止，它后面的语句都不执行。通过throw抛出异常后，如果想在上一级代码中来捕获并处理异常，则需要在抛出异常的方法中使用throws关键字在方法声明中指明要跑出的异常；如果要捕捉throw抛出的异常，则必须使用try—catch语句。举例如下：
<span class="kwd">class</span><span class="pln"> </span><span class="typ">MyException</span><span class="pln"> </span><span class="kwd">extends</span><span class="pln"> </span><span class="typ">Exception</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="com">//创建自定义异常类</span><span class="pln"> </span><span class="typ">String</span><span class="pln"> message</span><span class="pun">;</span><span class="pln"> </span><span class="com">//定义String类型变量</span><span class="pln"> </span><span class="kwd">public</span><span class="pln"> </span><span class="typ">MyException</span><span class="pun">(</span><span class="typ">String</span><span class="pln"> </span><span class="typ">ErrorMessagr</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="com">//父类方法</span><span class="pln"> message </span><span class="pun">=</span><span class="pln"> </span><span class="typ">ErrorMessagr</span><span class="pun">;</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">public</span><span class="pln"> </span><span class="typ">String</span><span class="pln"> getMessage</span><span class="pun">(){</span><span class="pln"> </span><span class="com">//覆盖getMessage()方法</span><span class="pln"> </span><span class="kwd">return</span><span class="pln"> message</span><span class="pun">;</span><span class="pln"> </span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Captor</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="com">//创建类</span><span class="pln"></span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">int</span><span class="pln"> quotient</span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> x</span><span class="pun">,</span><span class="kwd">int</span><span class="pln"> y</span><span class="pun">)</span><span class="pln"> </span><span class="kwd">throws</span><span class="pln"> </span><span class="typ">MyException</span><span class="pun">{</span><span class="com">//定义方法抛出异常</span><span class="pln"></span><span class="kwd">if</span><span class="pun">(</span><span class="pln">y </span><span class="pun"><</span><span class="pln"> </span><span class="lit">0</span><span class="pun">){</span><span class="pln"> </span><span class="com">//判断参数是否小于0</span><span class="pln"> </span><span class="kwd">throw</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">MyException</span><span class="pun">(</span><span class="str">"除数不能是负数"</span><span class="pun">);</span><span class="com">//异常信息</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">return</span><span class="pln"> x</span><span class="pun">/</span><span class="pln">y</span><span class="pun">;</span><span class="com">//返回值</span><span class="pln"> </span><span class="pun">}</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> main</span><span class="pun">(</span><span class="typ">String</span><span class="pln"> args</span><span class="pun">[]){</span><span class="pln"> </span><span class="com">//主方法</span><span class="pln"> </span><span class="kwd">try</span><span class="pun">{</span><span class="pln"> </span><span class="com">//try语句包含可能发生异常的语句</span><span class="pln"> </span><span class="kwd">int</span><span class="pln"> result </span><span class="pun">=</span><span class="pln"> quotient</span><span class="pun">(</span><span class="lit">3</span><span class="pun">,-</span><span class="lit">1</span><span class="pun">);</span><span class="com">//调用方法quotient()</span><span class="pln"> </span><span class="pun">}</span><span class="kwd">catch</span><span class="pln"> </span><span class="pun">(</span><span class="typ">MyException</span><span class="pln"> e</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="com">//处理自定义异常</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="pln">e</span><span class="pun">.</span><span class="pln">getMessage</span><span class="pun">());</span><span class="pln"> </span><span class="com">//输出异常信息</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">catch</span><span class="pln"> </span><span class="pun">(</span><span class="typ">ArithmeticException</span><span class="pln"> e</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="com">//处理ArithmeticException异常</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"除数不能为0"</span><span class="pun">);</span><span class="com">//输出提示信息</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">catch</span><span class="pln"> </span><span class="pun">(</span><span class="typ">Exception</span><span class="pln"> e</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="com">//处理其他异常</span><span class="pln"> </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"程序发生了其他的异常"</span><span class="pun">);</span><span class="pln"> </span><span class="com">//输出提示信息</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span> |
