private String chooseFiles() {
IProject project = MuClipsePlugin.getProject(txtProject.getText().trim());
IFolder input = project.getFolder(txtSelectedFolderSource.getText());
final ElementTreeSelectionDialog dialog =
new ElementTreeSelectionDialog(getShell(),
new FileLabelProvider(),
new FileTreeContentProvider(false));
dialog.setAllowMultiple(true);
dialog.setTitle("MuClipse");
dialog.setMessage("Select a java class");
dialog.setInput(input);