Bug 9304 new class wizard: incorrect terminology used
1. new class wizard 2. press Add.. in interfaces 3. the dialog you see has a title 'Extended Interfaces Selection' this is incorrect - it should be 'Implemented Interfaces Selection' (this bug was pointed out on the wsad newsgroup)
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/TypePage.java
status.setError(NewWizardMessages.getString("TypePage.error.EnclosingTypeEnterName")); 
			return status;
		}
		try {
			IType type= JavaModelUtil.findType(root.getJavaProject(), enclName);
			if (type == null) {
				status.setError(NewWizardMessages.getString("TypePage.error.EnclosingTypeNotExists")); 
				return status;
			}
			if (type.getCompilationUnit() == null) {
				status.setError(NewWizardMessages.getString("TypePage.error.EnclosingNotInCU")); 
				return status;
			}
			fCurrEnclosingType= type;
			IPackageFragmentRoot enclosingRoot= JavaModelUtil.getPackageFragmentRoot(type);
			if (!enclosingRoot.equals(root)) {
				status.setWarning(NewWizardMessages.getString("TypePage.warning.EnclosingNotInSourceFolder")); 
			}
			return status;
		} catch (JavaModelException e) {
			status.setError(NewWizardMessages.getString("TypePage.error.EnclosingTypeNotExists")); 
			JavaPlugin.log(e.getStatus());
			return status;
		}
	}
	
	/**
	 * Called when the type name has changed.
	 * The method validates the type name and returns the status of the validation.
	 * Can be extended to add more validation