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
IResource res= fWorkspaceRoot.findMember(new Path(fRootDialogField.getText()));
		if (res != null) {
			dialog.setInitialSelection(res);
		}
		if (dialog.open() == dialog.OK) {
			return (IFolder) dialog.getFirstResult();
		}			
		return null;		
	}
	private IJavaProject chooseProject() {
		IJavaProject[] projects;
		try {
			projects= JavaCore.create(fWorkspaceRoot).getJavaProjects();
		} catch (JavaModelException e) {
			JavaPlugin.log(e);
			projects= new IJavaProject[0];
		}
		
		ILabelProvider labelProvider= new JavaElementLabelProvider(JavaElementLabelProvider.SHOW_DEFAULT);
		ElementListSelectionDialog dialog= new ElementListSelectionDialog(getShell(), labelProvider);
		dialog.setTitle(NewWizardMessages.getString("NewSourceFolderWizardPage.ChooseProjectDialog.title")); 
		dialog.setMessage(NewWizardMessages.getString("NewSourceFolderWizardPage.ChooseProjectDialog.description")); 
		dialog.setElements(projects);
		dialog.setInitialSelections(new Object[] { fCurrJProject });
		if (dialog.open() == dialog.OK) {			
			return (IJavaProject) dialog.getFirstResult();
		}			
		return null;		
	}