C++中异常:
1、可以抛出任何异常。虽然标准C++定义了std::exception类,但throw的对象可以是任何对象。包括int、char*等。例如:
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但是,C++标准库中抛出的所有异常,都是派生自std::exception类。
std::exception定义如下:
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2、标准C++中,是没有finally子句。熟悉Java和C#的朋友,也许会觉得奇怪!没有finally子句,使用的确不方便。
3、C++中,函数的声明,缺省时可以抛出任何异常的,也可以使用异常规范来约束函数抛出的异常,如:
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但是,C++中的异常规范不是很可靠。如下的代码也是可以编译通过的,但是编译器会给出警告。
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4、C++的异常可以派生自多个异常基类。这一个特性使得难以分类的异常容易处理,例如网络文件的异常:
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5、捕捉所有异常的语法。C++中,不是单根继承的,所以你不能,如同Java或者C#那样,通过捕捉某个基类来捕捉所有的异常。
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总结,C++中,命名空间和异常规范是作为针对大规模程序设计而引入的特性。但是由于C++中没有垃圾收集机制,异常造成了资源管理变得非常复杂。在C++中,编写异常安全的代码,是十分困难的。
Java中的异常:
1、可以抛出任何派生自了Throwable的类。Throwable类的定义如下:
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Throwable下分Exception和Error。
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而Exception中,有一个特别的派生类,RuntimeException,如下:
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类图如下:
2、Java中,也使用异常规范,并且在整个基础类库中都使用。Java是基于JVM运行,但是JVM本身就抛出异常,也就是,所有的方法都可能抛出异常。因此,Java编译器编译不检查Error和RuntimeException。与C++不同,没有异常规范,缺省不允许抛出任何非RuntimeException和Error的异常。如下:
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以下的代码编译出错
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使用异常规范的正确例子:
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3、Throwable、Exception、RuntimeException中部分成员,是在不同的JDK版本中添加的,编写代码的时候需要注意。如下的代码不能在JDK 1.3中编译通过:
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4、Java中的try语法,包括finally子句。如下:
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C#中的异常:
1、C#异常的局限性。C#是基于CLR运行的,由于CLR需要支持多种语言,其异常的实现受到了较大的局限。一个重要的特征就是没有异常规范,很多人对此很失望!Anders Hejlsberg曾专门发表过文章,说明为什么C#不支持异常规范,说得也很有道理。但是,没有异常规范的C#,变得简单,但也更容易犯错误,在这一点上,我更喜欢Java,而不喜欢C#的方式。没有异常规范,编译器就不会帮我们检查代码,是否做了try ... catch处理。
2、异常的结构。在.NET Framework中,所有的异常派生自System.Exception基类。其下有两个子类:SystemException和ApplicationException。自行编写异常类,不建议直接派生自Exception类,而是应该派生自ApplicationException。
3、C#犹如Java,也支持finally的写法。如:
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