@Nullable
public static String checkFunctionalInterface(
@NotNull PsiAnnotation annotation, @NotNull LanguageLevel languageLevel) {
if (languageLevel.isAtLeast(LanguageLevel.JDK_1_8)
&& Comparing.strEqual(annotation.getQualifiedName(), JAVA_LANG_FUNCTIONAL_INTERFACE)) {
final PsiAnnotationOwner owner = annotation.getOwner();
if (owner instanceof PsiModifierList) {
final PsiElement parent = ((PsiModifierList) owner).getParent();
if (parent instanceof PsiClass) {
return LambdaHighlightingUtil.checkInterfaceFunctional(
(PsiClass) parent, ((PsiClass) parent).getName() + " is not a functional interface");
}
}
}
return null;
}
