File.list() vs File.listFiles()

Question

My question is: if this two functions have something different? I mean I know that they return something different, but is it possible that number of elements in one would be different then in the second one. I will try to explain. I implemented TreeModel for one of my class trying to make nice view on files on the PC basing on JTree. So here is the part of it:

public Object getChild(Object parent, int index) {
        File[] children = ((File) parent).listFiles();
        if(children == null || index < 0 || index >= children.length) {
            return null;
        }

        File result = new MyFile(children[index]);
        return result;
}

public int getChildCount(Object parent) {
        //---
        //String[] children = ((File)parent).list();
        File[] children = ((File)parent).listFiles();
        //---

        if(children == null) {
            return 0;
        }
        return children.length;
}

I marked interesting code. If I changed this two lines for this commented one, sometimes I get NullPointerException after loading TreeModel: jtree.setModel(treeModel);. This uncommented does not cause any trouble. I checked the docs and it says nothing unusual including returning null by both methods. What is going on here?

Answer 1

Both methods do essentially the same, look at http://www.docjar.com/html/api/java/io/File.java.html for details.

Answer 2

As already pointed, but clarified only within the comments in post from D.R

• list method returns String array with filenames (files and directories)

• listFiles return array of class File of the same

See doc pages, eg. https://docs.oracle.com/javase/7/docs/api/java/io/File.html

String[] list() Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname.

File[] listFiles() Returns an array of abstract pathnames denoting the files in the directory denoted by this abstract pathname.

I am not sure why both methods exist, probably String array will be faster and less memory consuming than File array one