Java File Handling, what did I do wrong?

Question

Wrote up a basic file handler for a Java Homework assignment, and when I got the assignment back I had some notes about failing to catch a few instances:

• Buffer from file could have been null.
• File was not found
• File stream wasn't closed

Here is the block of code that is used for opening a file:

/**
 * Create a Filestream, Buffer, and a String to store the Buffer.
 */
FileInputStream fin = null;
BufferedReader buffRead = null;
String loadedString = null;

/** Try to open the file from user input */
try
{
    fin = new FileInputStream(programPath + fileToParse);
    buffRead = new BufferedReader(new InputStreamReader(fin));
    loadedString = buffRead.readLine();
    fin.close();
}
/** Catch the error if we can't open the file */
catch(IOException e)
{
    System.err.println("CRITICAL: Unable to open text file!");
    System.err.println("Exiting!");
    System.exit(-1);
}

The one comment I had from him was that fin.close(); needed to be in a finally block, which I did not have at all. But I thought that the way I have created the try/catch it would have prevented an issue with the file not opening.

Let me be clear on a few things: This is not for a current assignment (not trying to get someone to do my own work), I have already created my project and have been graded on it. I did not fully understand my Professor's reasoning myself. Finally, I do not have a lot of Java experience, so I was a little confused why my catch wasn't good enough.

Answer 1

• Buffer from file could have been null.

The file may be empty. That is, end-of-file is reach upon opening the file. loadedString = buffRead.readLine() would then have returned null.

Perhaps you should have fixed this by adding something like if (loadedString == null) loadedString = "";

• File was not found

As explained in the documentation of the constructor of FileInputStream(String) it may throw a FileNotFoundException. You do catch this in your IOException clause (since FileNotFoundException is an IOException), so it's fine, but you could perhaps have done:

} catch (FileNotFoundException fnfe) {
    System.err.println("File not fonud!");
} catch (IOException ioex {
    System.err.println("Some other error");
}

• File stream wasn't closed

You do call fin.close() which in normal circumstances closes the file stream. Perhaps he means that it's not always closed. The readLine could potentially throw an IOException in which case the close() is skipped. That's the reason for having it in a finally clause (which makes sure it gets called no matter what happens in the try-block. (*)

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(*) As @mmyers correctly points out, putting the close() in a finally block will actually not be sufficient since you call System.exit(-1) in the catch-block. If that really is the desired behavior, you could set an error flag in the catch-clause, and exit after the finally-clause if this flag is set.