Draw lines in binary tree graphical representation

Question

I’m trying to draw a binary tree using swing and awt in java. I can already show the knots of the tree but I’m not able to draw the lines of a parent knot to your children. I have the Node, Treegui, Drawtree and Main classes. This image is how the output is without the lines.

My intention is to show lines from a parent node to your child nodes. I tried to use the method drawLine class Graphics but it stayed that way:

The drawTree method defines the position of the values of the nodes on the screen and stores the position of the nodes in Arraylists. The drawLine method draws the lines. I believe the lines are that way because the values are stored in that particular order. I have tried several ways and I cannot connect the lines correctly. How can I show the lines only from a parent to their children?

public class TreeGUI extends JFrame {

    private JPanel contentPane;
    public Node node;
    public DrawTree drawer;

    /**
     * Create the frame.
     */
    public TreeGUI(Node node) {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 500, 500);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        drawer = new DrawTree(node);
        contentPane.add(drawer);
        setContentPane(contentPane);
        this.node = node;
        setVisible(true);
    }

}

class DrawTree extends JPanel{

    public Node node;
    public static ArrayList listX = new ArrayList();
    public static ArrayList listY = new ArrayList();


    public DrawTree(Node node){
        this.node = node;
    }

    @Override
    protected void paintComponent(Graphics g) {
        // TODO Auto-generated method stub
        g.setFont(new Font("Tahoma", Font.BOLD, 20));
        DrawTree(g, 0, getWidth(), 0, getHeight() / node.getheight(node), node);
        listX.clear();
        listY.clear();
    }

    public void DrawTree(Graphics g, int StartWidth, int EndWidth, int StartHeight, int Level, Node node) {
        String data = String.valueOf(node.getValue());
        g.setFont(new Font("Tahoma", Font.BOLD, 20));
        FontMetrics fm = g.getFontMetrics();
        int dataWidth = fm.stringWidth(data);

        g.drawString(data, (StartWidth + EndWidth) / 2 - dataWidth / 2, StartHeight + Level / 2);
        listX.add((StartWidth + EndWidth) / 2 - dataWidth / 2);
        listY.add(StartHeight + Level / 2);
        drawLine(g, node);

        if (node.getLeft() != null) {
            DrawTree(g, StartWidth, (StartWidth + EndWidth) / 2, StartHeight + Level, Level, node.getLeft());
        }
        if (node.getRight() != null)
            DrawTree(g, (StartWidth + EndWidth) / 2, EndWidth, StartHeight + Level, Level, node.getRight());
    }

public void drawLine(Graphics g,  Node node){
       for (int i=1; i < listY.size(); i++)
            g.drawLine((int)listX.get(i-1), (int)listY.get(i-1), (int)listX.get(i), (int)listY.get(i));
    }

}

main method

public static void main(String[] args) {
    Node raiz = null;
    raiz = raiz.insert(raiz, 35);
    raiz.insert(raiz, 25);
    raiz.insert(raiz, 75);
    raiz.insert(raiz, 30);
    raiz.insert(raiz, 20);
    raiz.insert(raiz, 12);
    raiz.insert(raiz, 6);
    raiz.insert(raiz, 23);
    raiz.insert(raiz, 90);
    TreeGUI gui = new TreeGUI(raiz);
}

Answer 1

Try with these modifications that I made, it will probably work, I tested with a Tree class that had already implemented and worked, I hope to have helped.

public void DrawTree(Graphics g, int StartWidth, int EndWidth, int StartHeight, int Level, Node node) {
    String data = String.valueOf(node.getValue());
    g.setFont(new Font("Tahoma", Font.BOLD, 20));
    FontMetrics fm = g.getFontMetrics();
    int dataWidth = fm.stringWidth(data);

    g.drawString(data, (StartWidth + EndWidth) / 2 - dataWidth / 2, StartHeight + Level / 2);
    listX.add((StartWidth + EndWidth) / 2 - dataWidth / 2);
    listY.add(StartHeight + Level / 2);
    drawLine(g, node);

    //Imprime as linhas que ligam os nós a seus filhos
    if(listX.size() > 1){
        g.drawLine((int)listX.get(listX.size()-2), (int)listY.get(listY.size()-2), (int)listX.get(listX.size()-1), (int)listY.get(listY.size()-1));
    }

    if (node.getLeft() != null) {
        DrawTree(g, StartWidth, (StartWidth + EndWidth) / 2, StartHeight + Level, Level, node.getLeft());
    }

    if (node.getRight() != null){

         /*Como a recursão visita os nós da esquerda primeiro, se o nó que está sendo tratado for o filho à direira e
            houver filho(s) à esquerda, quer dizer que os filhos à esquerda já foram visitados e suas linhas já foram 
            desenhadas, ou seja, seus pontos devem ser removidos, para evitar que sejam desenhados outra vez. 
         */
        if (listX.size() > 1 && node.getLeft() != null) {
            for(int i = 0; i < node.getLeft().getHeight(); i++){
                listX.remove(listX.size()-1);
                listY.remove(listY.size()-1);
            }
        }
        DrawTree(g, (StartWidth + EndWidth) / 2, EndWidth, StartHeight + Level, Level, node.getRight());
    }
}