@Nullable private String verifyInnerClassDestination() { PsiClass targetClass = findTargetClass(); if (targetClass == null) return null; for (PsiElement element : myElementsToMove) { if (PsiTreeUtil.isAncestor(element, targetClass, false)) { return RefactoringBundle.message("move.class.to.inner.move.to.self.error"); } final Language targetClassLanguage = targetClass.getLanguage(); if (!element.getLanguage().equals(targetClassLanguage)) { return RefactoringBundle.message( "move.to.different.language", UsageViewUtil.getType(element), ((PsiClass) element).getQualifiedName(), targetClass.getQualifiedName()); } if (element.getLanguage().equals(Language.findLanguageByID("Groovy"))) { return RefactoringBundle.message("dont.support.inner.classes", "Groovy"); } } while (targetClass != null) { if (targetClass.getContainingClass() != null && !targetClass.hasModifierProperty(PsiModifier.STATIC)) { return RefactoringBundle.message("move.class.to.inner.nonstatic.error"); } targetClass = targetClass.getContainingClass(); } return null; }