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
/** 
	 * @see NewElementWizardPage#getRunnable
	 */	
	public IRunnableWithProgress getRunnable() {
		return new IRunnableWithProgress() {
			public void run(IProgressMonitor monitor) throws InvocationTargetException {
				try {
					fCreatedRoot= createPackageFragmentRoot(monitor, getShell());
				} catch (CoreException e) {
					throw new InvocationTargetException(e);
				} 
			}
		};
	}
	
	protected IPackageFragmentRoot getNewPackageFragmentRoot() {
		return fCreatedRoot;
	}
	
	
	protected IPackageFragmentRoot createPackageFragmentRoot(IProgressMonitor monitor, Shell shell) throws CoreException {
		String relPath= fRootDialogField.getText();
			
		IFolder folder= fCurrJProject.getProject().getFolder(relPath);
		IPath path= folder.getFullPath();
		if (!folder.exists()) {
			CoreUtility.createFolder(folder, true, true, monitor);			
		}