private static void addCurrentlySelectedItemToTop(
     Lookup lookup, List<LookupElement> items, LinkedHashSet<LookupElement> model) {
   if (!lookup.isSelectionTouched()) {
     LookupElement lastSelection = lookup.getCurrentItem();
     if (ContainerUtil.indexOfIdentity(items, lastSelection) >= 0) {
       model.add(lastSelection);
     }
   }
 }
  @Override
  public Result acceptChar(char c, final int prefixLength, final Lookup lookup) {
    if (!lookup.getPsiFile().getLanguage().isKindOf(JavaLanguage.INSTANCE)) {
      return null;
    }

    LookupElement item = lookup.getCurrentItem();
    if (item == null) return null;

    final Object o = item.getObject();
    if (c == '!') {
      if (o instanceof PsiVariable) {
        if (PsiType.BOOLEAN.isAssignableFrom(((PsiVariable) o).getType()))
          return Result.SELECT_ITEM_AND_FINISH_LOOKUP;
      }
      if (o instanceof PsiMethod) {
        final PsiType type = ((PsiMethod) o).getReturnType();
        if (type != null && PsiType.BOOLEAN.isAssignableFrom(type))
          return Result.SELECT_ITEM_AND_FINISH_LOOKUP;
      }
      if (o instanceof PsiKeyword && ((PsiKeyword) o).textMatches(PsiKeyword.INSTANCEOF)) {
        return Result.SELECT_ITEM_AND_FINISH_LOOKUP;
      }

      return null;
    }
    if (c == '.' && isWithinLiteral(lookup)) return Result.ADD_TO_PREFIX;

    if (c == ':') {
      PsiFile file = lookup.getPsiFile();
      PsiDocumentManager.getInstance(file.getProject())
          .commitDocument(lookup.getEditor().getDocument());
      PsiElement leaf = file.findElementAt(lookup.getEditor().getCaretModel().getOffset() - 1);
      if (PsiUtil.getLanguageLevel(file).isAtLeast(LanguageLevel.JDK_1_8)) {
        PsiStatement statement = PsiTreeUtil.getParentOfType(leaf, PsiStatement.class);
        if (statement == null
            || statement.getTextRange().getStartOffset()
                != leaf.getTextRange().getStartOffset()) { // not typing a statement label
          return Result.SELECT_ITEM_AND_FINISH_LOOKUP;
        }
      }
      if (PsiTreeUtil.getParentOfType(leaf, PsiSwitchLabelStatement.class) != null
          || PsiTreeUtil.getParentOfType(leaf, PsiConditionalExpression.class) != null) {
        return Result.SELECT_ITEM_AND_FINISH_LOOKUP;
      }
      return Result.HIDE_LOOKUP;
    }

    if (c == '[' || c == ']' || c == ')' || c == '>')
      return CharFilter.Result.SELECT_ITEM_AND_FINISH_LOOKUP;
    if (c == '<' && o instanceof PsiClass) return Result.SELECT_ITEM_AND_FINISH_LOOKUP;
    if (c == '(') {
      if (o instanceof PsiClass) {
        if (PsiJavaPatterns.psiElement()
            .afterLeaf(PsiKeyword.NEW)
            .accepts(lookup.getPsiElement())) {
          return Result.SELECT_ITEM_AND_FINISH_LOOKUP;
        }
        return Result.HIDE_LOOKUP;
      }
      if (o instanceof PsiType) {
        return Result.HIDE_LOOKUP;
      }
    }
    if ((c == ',' || c == '=') && o instanceof PsiVariable) {
      int lookupStart = lookup.getLookupStart();
      String name = ((PsiVariable) o).getName();
      if (lookupStart >= 0 && name != null && name.equals(lookup.itemPattern(item))) {
        return Result.HIDE_LOOKUP;
      }
    }

    if (c == '#'
        && PsiTreeUtil.getParentOfType(lookup.getPsiElement(), PsiDocComment.class) != null) {
      if (o instanceof PsiClass) {
        return Result.SELECT_ITEM_AND_FINISH_LOOKUP;
      }
    }
    if (c == '(' && PsiKeyword.RETURN.equals(item.getLookupString())) {
      return Result.HIDE_LOOKUP;
    }
    return null;
  }