2-3+ tree dot output

gistfile1.java

    private String dotNode(BaseNode node){
        String dotNode = "\n    \"" + ((Object)node).toString() + "\" [label=<<table><tr><td port=\"l\">";
        if (node instanceof InternalNode) {
            dotNode += (((InternalNode)node).left == null) ? "null" : ((InternalNode)node).left;
            dotNode += "\n        </td><td port=\"n\">";
            dotNode += ((Object)node).toString();
            dotNode += "\n        </td><td port=\"r\">";
            dotNode += (((InternalNode)node).right == null) ? "null" : ((InternalNode)node).right;
            dotNode += "\n        </td></tr><tr><td port=\"cl\">";
            dotNode += (((InternalNode)node).childleft == null) ? "null" : ((Object)((InternalNode)node).childleft).toString();
            dotNode += "\n        </td><td port=\"cc\">";
            dotNode += (((InternalNode)node).childcenter == null) ? "null" : ((Object)((InternalNode)node).childcenter).toString();
            dotNode += "\n        </td><td port=\"cr\">";
            dotNode += (((InternalNode)node).childright == null) ? "null" : ((Object)((InternalNode)node).childright).toString();
        } else {
            dotNode += (((LeafNode)node).left == null) ? "null" : ((LeafNode)node).left;
            dotNode += "\n        </td><td port=\"n\">";
            dotNode += ((Object) node).toString();
            dotNode += "\n        </td><td port=\"r\">";
            dotNode += (((LeafNode)node).right == null) ? "null" : ((LeafNode)node).right;
        }
        dotNode += "\n        </td></tr></table>>];\n";
        return dotNode;
    }

    public String graph(){
        Set<BaseNode> visited = new HashSet<>();
        LinkedList<BaseNode> queue = new LinkedList<>();
        String dot = "digraph \"2-3+tree\" {\n    node [shape=plaintext]";
        if (root != null) queue.addLast(root);
        BaseNode current;
        while (!queue.isEmpty()) {
            current = queue.pop();
            if (!visited.add(current)) continue;
            dot += dotNode(current);

            if (current instanceof InternalNode) {
                if (((InternalNode)current).childleft != null) {
                    dot += '"' + ((Object) current).toString() + "\":cl -> \"" + ((Object) ((InternalNode) current).childleft).toString() + "\"\n";
                    queue.addLast(((InternalNode)current).childleft);
                }
                if (((InternalNode)current).childcenter != null) {
                    dot += '"' + ((Object) current).toString() + "\":cc -> \"" + ((Object) ((InternalNode) current).childcenter).toString() + "\"\n";
                    queue.addLast(((InternalNode)current).childcenter);
                }
                if (((InternalNode)current).childright != null) {
                    dot += '"' + ((Object) current).toString() + "\":cr -> \"" + ((Object) ((InternalNode) current).childright).toString() + "\"\n";
                    queue.addLast(((InternalNode)current).childright);
                }
            }
        }
        return dot + "\n}";
    }

    public String writeGraph(){
        StringUtils.writeFile(this.graph(), "last test graph.dot");
        return this.toString();
    }

        public static void writeFile(String string, String filename) {
        try {
            FileWriter file = new FileWriter(filename);
            file.write(string);
            file.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }