Why won't JPanel show up in an external JFrame?

Question

My code generates a graph and displays it in a JPanel.
If the class extends JFrame, the output looks exactly as it should. The problem is that I need to extend it as a JPanel so that I can imbed it in another GUI. When I modify the code so that it is a JPanel, the graph does not show up at all (except a tiny little smudge).
What am I missing? Here is a trimmed down version:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
* @author Rob Kallman <[email protected]>
public class GraphSSCCE extends JPanel {
     protected JPanel mainPanel;
     protected JPanel graphPanel;
     protected final int FRAME_PANEL_WIDTH = 950;
     protected final int FRAME_PANEL_HEIGHT = 400;     
     protected final int GRAPH_PANEL_WIDTH = 950;
     protected final int GRAPH_PANEL_HEIGHT = 400;
     protected final int NODE_COUNT = 3;
     protected final int node_d = 30;
     protected int centerX = GRAPH_PANEL_WIDTH/2;
     protected int centerY = GRAPH_PANEL_HEIGHT/2;
     protected java.util.List<Node> nodes = new ArrayList<Node>(NODE_COUNT);
     public GraphSSCCE() {
          //super("Graph Redux");
          this.setSize(FRAME_PANEL_WIDTH,FRAME_PANEL_HEIGHT);
          //this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          mainPanel = new Graph();
          this.setBackground(Color.WHITE);
          this.add(mainPanel);
     public static void main(String args[]) {
          JFrame frame = new JFrame("Graph Test");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          GraphSSCCE gr = new GraphSSCCE();
          frame.setSize(gr.getSize());
          frame.add(gr);
          frame.setVisible(true);
@SuppressWarnings("serial")
class Graph extends JPanel {
     public Graph() {
          super();
          graphPanel = new JPanel();
          graphPanel.setBackground(Color.WHITE);
          graphPanel.setSize(GRAPH_PANEL_WIDTH, GRAPH_PANEL_HEIGHT);
          repaint();
     public void paint(Graphics g) {
          super.paint(g);
          int graphW = graphPanel.getWidth() - 100;
          int graphH = graphPanel.getHeight() - 100;
          //Draw Root node
          Node root = new Node(0, (graphPanel.getWidth() - 100)/4, graphH/2 + 20, node_d);
          g.setColor(Color.BLACK);
          g.fillOval(root.x-2, root.y-2, root.d + 4, root.d + 4);
          g.setColor(Color.RED);
          g.fillOval(root.x, root.y, root.d , root.d);
          //Draw site nodes
          for(int i = 0; i < NODE_COUNT; i++) {
               double nc = NODE_COUNT;
               double frac = i/(nc-1);
               Node node = new Node(i, 3*(graphW)/4, (int)(frac * graphH) + 20 + (int)frac, node_d);
               nodes.add(i, node);  // An ArrayList that contains all of the Node objects.
          // Populate network with edges from root to site     
               for(Node noodle : nodes) {
                    g.setColor(Color.BLACK);
                    g.drawLine(root.x + root.d/2, root.y + root.d/2, noodle.x + noodle.d/2, noodle.y + noodle.d/2);
                    g.setColor(Color.BLACK);
                    g.fillOval(noodle.x - 2, noodle.y - 2, noodle.d + 4, noodle.d + 4);
                    g.setColor(Color.RED);
                    g.fillOval(noodle.x, noodle.y, noodle.d, noodle.d);
               g.setColor(Color.BLACK);
               g.fillOval(root.x - 2, root.y - 2, root.d + 4, root.d + 4);
               g.setColor(Color.RED);  // Root
               g.fillOval(root.x, root.y, root.d, root.d);
class Node {
     protected int d;
     protected int x;
     protected int y;
     protected int node_id;
     public Node(int id, int x, int y, int d) {
          this.node_id = id;
          this.d = d;
          this.x = x;
          this.y = y;
}

Answer 1

Welcome to the Sun forums.
>
What am I missing? ...>That code was doing some odd things. Once I'd trimmed it down far enough to get it working, I'd made a number of undocumented changes. Have a look over this, and see if it get you back on track.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
* @author Rob Kallman <[email protected]>
public class GraphSSCCE extends JPanel {
     public static void main(String args[]) {
          JFrame frame = new JFrame("Graph Test");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          Graph gr = new Graph();
          JPanel mainPanel = new JPanel(new BorderLayout());
          mainPanel.add(gr, BorderLayout.CENTER);
          frame.setContentPane(mainPanel);
          frame.pack();
          frame.setSize(gr.getSize());
          frame.setVisible(true);
@SuppressWarnings("serial")
class Graph extends JPanel {
     protected final int FRAME_PANEL_WIDTH = 950;
     protected final int FRAME_PANEL_HEIGHT = 400;
     protected final int GRAPH_PANEL_WIDTH = 950;
     protected final int GRAPH_PANEL_HEIGHT = 400;
     protected final int NODE_COUNT = 3;
     protected final int node_d = 30;
     protected int centerX = GRAPH_PANEL_WIDTH/2;
     protected int centerY = GRAPH_PANEL_HEIGHT/2;
     protected java.util.List<Node> nodes = new ArrayList<Node>(NODE_COUNT);
     public Graph() {
          super();
          setBackground(Color.WHITE);
          repaint();
     public Dimension getPreferredSize() {
          return new Dimension(GRAPH_PANEL_WIDTH,GRAPH_PANEL_HEIGHT);
     /** Do not override paint() in a Swing component! */
     public void paintComponent(Graphics g) {
          super.paintComponent(g);
          g.setColor(getBackground());
          g.fillRect(0,0,getWidth(),getHeight());
          int graphW = getWidth() - 100;
          int graphH = getHeight() - 100;
          //Draw Root node
          Node root = new Node(0, (getWidth() - 100)/4, graphH/2 + 20, node_d);
          g.setColor(Color.BLACK);
          g.fillOval(root.x-2, root.y-2, root.d + 4, root.d + 4);
          g.setColor(Color.RED);
          g.fillOval(root.x, root.y, root.d , root.d);
          //Draw site nodes
          for(int i = 0; i < NODE_COUNT; i++) {
               double nc = NODE_COUNT;
               double frac = i/(nc-1);
               Node node = new Node(i, 3*(graphW)/4, (int)(frac * graphH) + 20 + (int)frac, node_d);
               nodes.add(i, node);  // An ArrayList that contains all of the Node objects.
          // Populate network with edges from root to site
               for(Node noodle : nodes) {
                    g.setColor(Color.BLACK);
                    g.drawLine(root.x + root.d/2, root.y + root.d/2, noodle.x + noodle.d/2, noodle.y + noodle.d/2);
                    g.setColor(Color.BLACK);
                    g.fillOval(noodle.x - 2, noodle.y - 2, noodle.d + 4, noodle.d + 4);
                    g.setColor(Color.RED);
                    g.fillOval(noodle.x, noodle.y, noodle.d, noodle.d);
               g.setColor(Color.BLACK);
               g.fillOval(root.x - 2, root.y - 2, root.d + 4, root.d + 4);
               g.setColor(Color.RED);  // Root
               g.fillOval(root.x, root.y, root.d, root.d);
class Node {
     protected int d;
     protected int x;
     protected int y;
     protected int node_id;
     public Node(int id, int x, int y, int d) {
          this.node_id = id;
          this.d = d;
          this.x = x;
          this.y = y;
}