Java - repaint() method is called once then it doesn't show anything

Question

I've been trying to get a n-ary tree structure graphed so when I enter some node it shows up but it doesn't.

It only draws the root then it "deletes" everything.

Here's my code:

public LinkedList<Node> nodes;
public Tree tree;

public TreeViewer() {

    initComponents();
    this.nodes = new LinkedList<>();
}

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g); //To change body of generated methods, choose Tools | Templates.

    if (this.tree != null) {
        this.checkTree(this.tree.getRoot(), g, 200, 20, 20, 20);
    }else{
        System.out.println("empty");
    }
}

public void checkTree(Node current, Graphics g, int x, int y, int height, int width) {

    current.setX(x);
    current.setY(y);
    current.setHeight(height);
    current.setWidth(width);

    if (!this.nodes.contains(current)) {
        g.drawString(current.name, x, y);
        g.setColor(Color.black);
        this.nodes.add(current);

        if (current.getSon() != null && current.getBrother() == null) {
            this.checkTree(current.getSon(), g, x, y + 40, height, width);

        } else if (current.getBrother() != null && current.getSon() == null) {
            this.checkTree(current.getBrother(), g, x - 30, y, height, width);

        } else if (current.getBrother() != null && current.getSon() != null) {
            this.checkTree(current.getSon(), g, x, y + 40, height, width);
            this.checkTree(current.getBrother(), g, x - 30, y, height, width);
        }
    }
}

and I'm adding the nodes trought a button, here's the code:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    if(this.modificator.getTree() == null){
        Node current = new Node(JOptionPane.showInputDialog("Type root ID:"));
        this.modificator.setTree( new Tree(current));

    }else{
        Node current = new Node(JOptionPane.showInputDialog("Type ID:"));
        this.modificator.getTree().addSon(this.modificator.getTree().getRoot(), this.modificator.getTree().getRoot(), current);

    }
    this.modificator.repaint();
}

So my problem resides in whenever I call repaint() after the first time, all that was drawn (only the root) gets "erased" from the panel.

When I draw a pre-instanced tree, it works, but I need it to draw it while I'm adding nodes at any moment of the running. — JMz, Apr 03 '16 at 07:19

score 3 · Accepted Answer · answered Apr 03 '16 at 07:19

Inside checkTree you have this:

if (!this.nodes.contains(current))

Presumably this is intended to handle cycles in your graph, but I don't see anywhere that clears this.nodes. That means that on the second call to paintComponent you immediately bail out of checkTree because the root has already been added to this.nodes.

If you clear out this.nodes at the end of paintComponent that might do the trick.

Java - repaint() method is called once then it doesn't show anything

1 Answers1