英文:
Exceptions from both try block and try-with-resources
问题
Documentation 中提到：
> 但在这个例子中，如果 readLine 和 close 方法都抛出异常，那么 readFirstLineFromFileWithFinallyBlock 方法会抛出从 finally 块抛出的异常；try 块抛出的异常会被抑制。相比之下，在例子 readFirstLineFromFile 中，如果异常同时从 try 块和 try-with-resources 语句中抛出，那么 readFirstLineFromFile 方法会抛出从 try 块抛出的异常；try-with-resources 语句中抛出的异常会被抑制。在 Java SE 7 及更高版本中，您可以检索被抑制的异常；有关更多信息，请参阅“被抑制的异常”部分。
我不理解加粗部分
> ... 如果异常同时从 try 块和 try-with-resources 语句中抛出 ...
如何同时从 try-with-resources 语句和 try 块抛出异常？如果异常是从 try-with-resources 语句中抛出的，那意味着资源初始化失败。在这种情况下，try 块永远不会执行。因此，前面的语句不可能发生。
我一定误解了这个 文档 和 try-with-resources 的工作方式。您能提供一个加粗语句实际发生的示例吗？
<hr>
提到的方法
static String readFirstLineFromFile(String path) throws IOException {
try (BufferedReader br =
new BufferedReader(new FileReader(path))) {
return br.readLine();
}
}
static String readFirstLineFromFileWithFinallyBlock(String path)
throws IOException {
BufferedReader br = new BufferedReader(new FileReader(path));
try {
return br.readLine();
} finally {
if (br != null) br.close();
}
}
英文:
Documentation says
> However, in this example, if the methods readLine and close both throw exceptions, then the method readFirstLineFromFileWithFinallyBlock throws the exception thrown from the finally block; the exception thrown from the try block is suppressed. In contrast, in the example readFirstLineFromFile, if exceptions are thrown from both the try block and the try-with-resources statement, then the method readFirstLineFromFile throws the exception thrown from the try block; the exception thrown from the try-with-resources block is suppressed. In Java SE 7 and later, you can retrieve suppressed exceptions; see the section Suppressed Exceptions for more information.
I don't understand the bold part
> ... if exceptions are thrown from both the try block and the try-with-resources statement ...
How can an exception be thrown from both the try-with-resources statement and the try block ? If the exception is thrown from the try-with-resources statement, it means that resource initialization failed. In this case, try block is never executed. Thus the previous statement can't happen.
I must have misunderstood this documentation and how try-with-resources works. Can you provide example where the bold statement actually happens ?
<hr>
Mentioned methods
static String readFirstLineFromFile(String path) throws IOException {
try (BufferedReader br =
new BufferedReader(new FileReader(path))) {
return br.readLine();
}
}
static String readFirstLineFromFileWithFinallyBlock(String path)
throws IOException {
BufferedReader br = new BufferedReader(new FileReader(path));
try {
return br.readLine();
} finally {
if (br != null) br.close();
}
}
答案1
得分: 2
如果异常从try-with-resources语句和try块都被抛出，那么这意味着资源初始化失败。try-with-resources语句不仅初始化资源，还关闭资源，关闭可能会引发异常。这句话紧随对使用try-finally时类似情况的描述，并将其与try-with-resources进行比较。
英文:
> How can an exception be thrown from both the try-with-resources statement and the try block ? If the exception is thrown from the try-with-resources statement, it means that resource initialization failed.
The try-with-resources statement not only initializes but also closes the resource, and closing may throw an exception.
This sentence comes right after a description of a similar situation when using try-finally, and compares it with try-with-resources.
答案2
得分: 0
Oracle文档不够好。我不会将"try-with-resources"块称为隐式关闭方法，而是称其为构造函数，文档没有提及构造函数中的异常。
英文:
oracle documentation sucks. i wouldn't call try-with-resources block for implicit close methods, but rather for constructors and doc doesn't say anything about exception in constructors
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