Finally & IOException

Question

Hi everybody,
I'm using InputStream for reading file. I know it's a good programming practice to close every InputStream when done with reading, to prevent any resource leaks. So i would use something like this:
InputStream is = null;
try {
      is = new FileInputStream(someFile);
} catch(IOException ioe) {
      // do something with exception...
} finally {
     // closing InputStream to prevent resource leaks
      if(is != null) {
                  is.close();
}My question is: What happens if an I/O error occurs while closeing InputStream i.e. close() method throws IOException? How could i get notified that an I/O error occurred? Should i also surround this method with a try-catch block e.g. something like this:
} finally {
     // closing InputStream to prevent resource leaks
      if(is != null) {
             try {
                  is.close();
             } catch (IOException e) {
                                System.out.println("Error", e);
}it looks like a solution to me, but now finally block looks a bit fuzzy.
Can anyone please help me about this topic...
Kind regards!
Igor

Answer 1

your said
The finally block contains the cleanup code to runafter the actual work code
here the creation of InputStream is part of actual
work code, but it's not inside the try-block.If that fails, there's nothing to clean up, since that's the very first step.
Nonetheless, I would tend to do it this way, because I consider it simpler and more consistent, even thoug it adds a couple steps that are not strictly necessary:
InputStream is = null;
try {
  is = new ... ;
  use is
finally {
  if (is != null) {
    try {
      is.close();
    catch (...) {
      log it
}And again, I'd put the entire body of the try block into a utilty method to keep things tidier.
I've tried and constructor does need the throws
clause, but my final question is:
Is it a good programming practice to put a method
with throws clause (without the surrounding try-catch
block) inside the construstor, 'casuse i've never
seen constructors with throws clause ?If you're considering a throws clause, that means it must be possible for some step in your c'tor to fail. So, given that, the question is, what do you do if that step fails? If that step is critical to putting the new object into a valid state, then you can't just let the c'tor complete normally without handling the exception. (Note that logging the exception does not count as handling it.) You need to either provide some other, failsafe, default initialization, or declare the exception.
There's nothing wrong with throwing an exception from the c'tor--it's the right thing to do if the c'tor can't complete its job properly.
Of course, you can take a step back and ask whether the stuff you're doing in the c'tor actually belongs there. A c'tor's job is to put the object into a valid working state. It should do that as completely as possible, but it shouldn't do anything more than that. So you have to decide, based on your object's job, whether it's necessary to process that file to get the object into a valid initial state.