java - 关于最终重抛

Question

我在 Precise Rethrow 的文档中读到，http://www.theserverside.com/tutorial/OCPJP-Use-more-precise-rethrow-in-exceptions-Objective-Java-7

Basically, you can list specific exceptions in the throws clause of your method, even if they are not explicitly handled by a catch block if:

The try block actually throws that specific exception at some point in time.

The specific Exception isn't already handled at any point by a preceding catch block

The exception named in the throws clause of the method signature must be on the class hierarchy of at least one exception being handled and rethrown by a catch block (subtype or supertype)

看一下代码(注意main的throws子句)

class OpenException extends Exception {}

class CloseException extends Exception {}

public class PRethrow
{
    public static void main(String args[]) throws OpenException, CloseException, java.io.IOException
    {
        boolean flag = true;
        try
        {
            if (flag)
            {
                throw new OpenException();
            }
            else
            {
                throw new CloseException();
            }
        }
        catch (Exception e)
        {
            System.out.println(e.getMessage());
            throw e;
        }
    } 
}

第一个条件中明确提到，如果 try block 在某个时间点实际抛出特定异常，则可以在 throws 子句中列出特定异常。

在我的代码中，try block 从不抛出 java.io.IOException，但仍将其包含在 throws 子句中不会产生任何错误。

为什么？

Answer 1

您提到的引用具有误导性:

• 如果在您的方法体中可能抛出检查异常，您必须在方法的 throws 子句中声明它。
• 但是您可以将任何异常添加到方法的throws 子句中，无论它是否真的可以被抛出。

例如这个编译:

public void m() throws IOException {}