CODEWITHSUNDEEP
javafilerecursionio
PetarMI
PetarMI

Reputation: 390

Find specific folder in Java

I am looking to find the path to a specific folder in Java as part of a bigger program.
What I have is a recursive function that checks every file that is contained within a starting directory and if it finds the folder I am looking for it assigns the path as a string to a variable. The following code works: 

//root is the starting directory and name is the folder I am looking for
private void findDir(File root, String name)  
{  
    if (root.getName().equals(name))
    {
        toFind = root.getAbsolutePath();
    }

    File[] files = root.listFiles();

    if(files != null)
    {
        for (File f : files)  
        {
            if(f.isDirectory())
            {   
                findDir(f, name);
            }
        }
    }
}

This works but I do not like the fact that I have to use the 'toFind' variable. My question is is there a way to make the method return a String instead of void? This will also save the program from checking all the other files in the system after finding the one it is looking for.
I was thinking of something like this but the following code will return null even if it finds the folder. 

private String findDir(File root, String name)
{
    if (root.getName().equals(name))
    {
        return root.getAbsolutePath();
    }

    File[] files = root.listFiles();

    if(files != null)
    {
        for (File f : files)  
        {
            if(f.isDirectory())
            {   
                return findDir(f, name);
            }
        }
    }

    return null; //???
}

Upvotes: 2

Views: 11765

Answers (1)

Sam
Sam

Reputation: 1206

This is because the first directory in your tree with no sub-directories will return null due to the fact that you specify that if the result for listFiles() is null, to return null for the entire recursion. It's not immediately obvious, but this can be fixed by changing the behavior in your for loop. Rather than directly returning a result inside your for loop, you should test if the result is null, and if so, just continue. If you however have a non-null result you can propagate the result upwards.

private String findDir(File root, String name)
{
    if (root.getName().equals(name))
    {
        return root.getAbsolutePath();
    }

    File[] files = root.listFiles();

    if(files != null)
    {
        for (File f : files)  
        {
            if(f.isDirectory())
            {   
                String myResult = findDir(f, name);
                //this just means this branch of the
                //recursion reached the end of the
                //directory tree without results, but
                //we don't want to cut it short here,
                //we still need to check the other
                //directories, so continue the for loop
                if (myResult == null) {
                    continue;
                }
                //we found a result so return!
                else {
                    return myResult;
                }
            }
        }
    }

    //we don't actually need to change this. It just means we reached
    //the end of the directory tree (there are no more sub-directories
    //in this directory) and didn't find the result
    return null;
}

Edit: Using Boris the Spider's suggestion, we could actually strip down the if statement to avoid the somewhat clunky nature of the continue statement, and make the code a little more to-the-point. Instead of:

if (myResult == null) {
    continue;
}
else {
    return myResult;
}

we could just slip in its place:

if (myResult != null) {
    return myResult;
}

which will evaluate with the same exact logic and takes less overall code.

Upvotes: 2

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