Is this file object left open?

Question

As an exercise for school I wrote a method in Java that searches for a character in a file. Here is the code:

 public static void countLetter(char needle, String hayStack) throws IOException {

        File f = new File(hayStack);                                           
        try (Scanner in = new Scanner(f)) {                                    
            String str = null;                                                 
            while (in.hasNext()){                                              
                str += in.next();                                              
            }                                                                  
            char[] charArr = str.toCharArray();                                
            int counter = 0;                                                   
            for (char c: charArr) {                                            
                if (c == needle){                                              
                    counter++;                                                 
                }                                                              
            }                                                                  
            System.out.println(counter);                                       
        }                                                                      
    }

This does what I need it to but I have a question. Is the file object ever opened? And if it is, does it ever closed? I used try-with-resources on the Scanner object so I'm pretty sure I don't have to explicitly close that, but what about the file object?

score 3 · Accepted Answer · answered May 06 '13 at 01:31

3

File object is just an abstract representation of a pathname, it has nothing to do with opening a file. So it can not be closed.

answered May 06 '13 at 01:31

Mukesh Kumar

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related question http://stackoverflow.com/questions/4752266/why-java-io-file-doesnt-have-a-close-method – Mukesh Kumar May 06 '13 at 01:32
I think your onto something here. – noel May 06 '13 at 01:33
As far as I can tell this is what it boils down to. Thanks for your perspective Mukesh. – noel May 06 '13 at 02:05

David Newcomb · Answer 2 · 2013-05-06T11:08:33.157

The File object can not be opened (and therefore can not be closed) as it is a representation of a file path and not a representation of a file.

The Scanner class opens your file in order to read it. Your program doesn't call in.close() so when your method returns the Scanner will not be garbage collected as it still has a reference to an open file. You may also be locking the file depending on how the file was opened by the Scanner.

In order for a class to qualify for automatically closing resources in a try-resource block the class must implement java.lang.AutoCloseable (or java.io.Closeable). Scanner does not implement these interfaces and so it won't have its close() method called when you exit the try-resource block.

Alter the code to:

public static void countLetter(char needle, String hayStack) throws IOException {

    File f = new File(hayStack);                                           
    try (Scanner in = new Scanner(f)) {                                    
        String str = null;                                                 
        while (in.hasNext()){                                              
            str += in.next();                                              
        }                                                                  
        char[] charArr = str.toCharArray();                                
        int counter = 0;                                                   
        for (char c: charArr) {                                            
            if (c == needle){                                              
                counter++;                                                 
            }                                                              
        }                                                                  
        System.out.println(counter);
        in.close();
    }
}

Which version are you looking at "Scanner.java:348", it's a comment line on mine. You might be referring to a section in the comments that says the scanner will close Closable's but you have to call close first as Scanner is itself *not* Closeable. The file opened inside the Scanner is not in scope and so won't be closed when you exit the try-resource block. — David Newcomb, May 06 '13 at 10:59

score 0 · Answer 3 · answered May 06 '13 at 01:26

0

As the variable is local to your function so it will go out of scope once the function exists, and eventually garbage collection. Answer to your question is NO, in your case file object is not ever opened.

answered May 06 '13 at 01:26

Juned Ahsan

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I don't think it's good to rely on contingencies to close files. I could be mistaken. – noel May 06 '13 at 01:27
Ideally you should close it. – Juned Ahsan May 06 '13 at 01:29

Is this file object left open?

3 Answers3

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