约书亚·布洛赫在《有效的Java》中说过

为以下情况使用检查异常 可恢复条件和运行时 编程错误的例外 (第二版第58项)

看看我理解的对不对。

以下是我对受控异常的理解:

try{
    String userInput = //read in user input
    Long id = Long.parseLong(userInput);
}catch(NumberFormatException e){
    id = 0; //recover the situation by setting the id to 0
}

1. 上述异常是否被认为是受控异常?

2. RuntimeException是未检查的异常吗?

以下是我对未检查异常的理解:

try{
    File file = new File("my/file/path");
    FileInputStream fis = new FileInputStream(file);   
}catch(FileNotFoundException e){

//3. What should I do here?
    //Should I "throw new FileNotFoundException("File not found");"?
    //Should I log?
    //Or should I System.exit(0);?
}

4. 现在,上面的代码不能也是一个受控异常吗?我可以试着挽回这样的局面吗?我可以吗?(注:我的第三个问题在上面的陷阱里)

try{
    String filePath = //read in from user input file path
    File file = new File(filePath);
    FileInputStream fis = new FileInputStream(file);   
}catch(FileNotFoundException e){
    //Kindly prompt the user an error message
    //Somehow ask the user to re-enter the file path.
}

5. 人们为什么要这样做?

public void someMethod throws Exception{

}

为什么他们让异常冒出来?早点处理错误不是更好吗?为什么要冒出来?

6. 我是否应该冒泡出确切的异常或使用异常掩盖它?

以下是我的阅读资料

在Java中,什么时候应该创建检查异常,什么时候应该是运行时异常?

何时选择已检查异常和未检查异常


当前回答

所有这些都是受控异常。未检查的异常是RuntimeException的子类。问题不在于如何处理它们,而在于你的代码是否应该抛出它们。如果你不想让编译器告诉你你还没有处理一个异常,那么你可以使用一个未检查的(RuntimeException的子类)异常。这些应该保存在你无法恢复的情况下,比如内存不足等。

其他回答

为什么他们让异常冒出来?早点处理错误不是更好吗?为什么要冒出来?

For example let say you have some client-server application and client had made a request for some resource that couldn't be find out or for something else error some might have occurred at the server side while processing the user request then it is the duty of the server to tell the client why he couldn't get the thing he requested for,so to achieve that at server side, code is written to throw the exception using throw keyword instead of swallowing or handling it.if server handles it/swallow it, then there will be no chance of intimating to the client that what error had occurred.

注意:为了清楚地描述发生的错误类型,我们可以创建自己的Exception对象并将其抛出给客户端。

检查异常:

The exceptions which are checked by the compiler for smooth execution of the program at runtime are called Checked Exception. These occur at compile time. If these are not handled properly, they will give compile time error (Not Exception). All subclasses of Exception class except RuntimeException are Checked Exception. Hypothetical Example - Suppose you are leaving your house for the exam, but if you check whether you took your Hall Ticket at home(compile time) then there won't be any problem at Exam Hall(runtime).

未检查异常:

The exceptions which are not checked by the compiler are called Unchecked Exceptions. These occur at runtime. If these exceptions are not handled properly, they don’t give compile time error. But the program will be terminated prematurely at runtime. All subclasses of RunTimeException and Error are unchecked exceptions. Hypothetical Example - Suppose you are in your exam hall but somehow your school had a fire accident (means at runtime) where you can't do anything at that time but precautions can be made before (compile time).

我认为受控异常对于使用外部库的开发人员是一个很好的提醒,在异常情况下,该库中的代码可能会出错。

需要指出的是,如果在代码中抛出一个受控异常,而catch在上面几层,则需要在您和catch之间的每个方法的签名中声明异常。因此,封装被破坏了,因为抛出路径中的所有函数都必须知道该异常的详细信息。

受控异常在编译时由JVM检查,并与资源相关(文件/db/流/套接字等)。受控异常的动机是,在编译时,如果资源不可用,应用程序应该在catch/finally块中定义一个替代行为来处理这个异常。

未经检查的异常纯粹是编程错误、错误计算、空数据甚至业务逻辑中的失败都可能导致运行时异常。在代码中处理/捕获未检查的异常是绝对没问题的。

解释摘自http://coder2design.com/java-interview-questions/