Bug 13034 Cannot create a Source Folder in a new Java Project
build 20020404 If you try and create a Source Folder in a Java Project you have just created you get an error preventing you from hitting finish. STEPS 1) Create Java Project Foo 2) Open New->Source Folder 3) Enter Bar as the name - you will get "Cannot nest entry Bar inside entry Foo/Bar" 4) Create a folder Bar. 5) Add it as a source folder in the Properties Dialog for Foo. No problem.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/NewSourceFolderWizardPage.java
public void init(IStructuredSelection selection) {
		if (selection == null || selection.isEmpty()) {
			setDefaultAttributes();
			return;
		}
		
		Object selectedElement= selection.getFirstElement();
		if (selectedElement == null) {
			selectedElement= EditorUtility.getActiveEditorJavaInput();
		}				
		
		String projPath= null;
		
		if (selectedElement instanceof IResource) {
			IProject proj= ((IResource)selectedElement).getProject();
			if (proj != null) {
				projPath= proj.getFullPath().makeRelative().toString();
			}	
		} else if (selectedElement instanceof IJavaElement) {
			IJavaProject jproject= ((IJavaElement)selectedElement).getJavaProject();
			if (jproject != null) {
				projPath= jproject.getProject().getFullPath().makeRelative().toString();
			}
		}	
		
		if (projPath != null) {
			fProjectField.setText(projPath);
			fRootDialogField.setText(""); 
		} else {
			setDefaultAttributes();