TreeContentProvider just getting every Directory of my path. (File Filter)

Question

im trying to get every folder of my path. Now Im getting just folders but as soon as some other file comes up it gives me a JavaNullPointerException. I know its beacuse of listFiles() but I dont know how to let it work otherwise. Can someone help me?

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@Override public Object[] getElements(Object inputElement) { return File.listRoots(); } @Override public Object getParent(Object element) { return ((File) element).getParentFile(); } @Override public boolean hasChildren(Object element) { Object[] obj = getChildren(element); return obj == null ? false : obj.length > 0; } @Override public Object[] getChildren(Object parentElement) { List<File> files = new ArrayList<>(); for (File file : ((File) parentElement).listFiles()) { if (file.isDirectory()) { files.add(file); } } return ((File) parentElement).listFiles(); }

Well listFiles returns null if the File is not a directory causing that error. You must check if it is directory before doing that. — greg-449
– greg-449, Commented Sep 10, 2020 at 16:19

greg-449 · Accepted Answer · 2020-09-10 19:09:16Z

File.listFiles() returns null if the file is not a directory. This is causing your exception.

To just show directories use something like:

@Override public Object[] getChildren(Object parentElement) { File parentFile = (File)parentElement; if (!parentFile.isDirectory()) { return new Object[0]; } return parentFile.listFiles(File::isDirectory); }

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