Newbie need help on JPanel graphics

hello gurus,
need your help. i'm so struggling on this program that i have to do. here's my scenario:
1) i have a frame that is divided by two JPanels, the left and right.
2) the right are subdivided by multiple jpanels and contains buttons and text.
when a button is pressed, it creates a text on the right panel.
3) the right works ok.
4) the left is "not" subdivided. it contains a couple of simple straight lines. and a clored background.
5) what i want to do is: to add additional lines to my left panel when a particular button is pressed from the right panel.
6) thats where im stuck. i'm played around with it but it either make my left drawings disappear or it makes a new panel. h

here's part of my code:

//this is in a different file.
public class LeftSide extends JPanel
{
public void paintComponent(Graphics g)
{
super.paintComponent(g);
setBackground(Color.GREEN);
}

public void paint(Graphics g)
{
super.paint(g);
g.drawLine(275, 50, 275, 500);
}
}

//this is also in a separate file.
private void createBodyGUIs()
{
setLayout(new BorderLayout());

biggerPanel.setLayout(new GridLayout(1,2));

add(biggerPanel, BorderLayout.CENTER);

LeftSide drawings = new LeftSide();
biggerPanel.add(drawings);
createRightColumnGUI(); //creates my goodies on the right side
}


thanks in advance!

Basically you need two panels first. In one of the panel you need two panels again. Do you design in that way?

See in this example code, how I handle the layouts.

Code:

---

    public PanelTest() {
        this.setLayout(new GridLayout(1, 2));
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(300, 300);
       
        JPanel one = new JPanel();
        one.add(new JButton("One"));
       
        JPanel two = new JPanel(new GridLayout(2, 1));
        two.add(new JButton("Two"));
        two.add(new JButton("Three"));
       
        this.add(one);
        this.add(two);
    }
   
    public static void main(String[] args) {
        new PanelTest().setVisible(true);
    }

---

hello eranga,
thank you for replying. basically, what i have is a frame with panel. that panel is divided in two, the left and the right. i have buttons on the right panel and they work perfectly. my problem is my left panel. i have a straight line drawn on it as you can see from my code. i would like to add another line to it everytime a particular button (from the right panel) is pressed.

i don't know how to do that. i don't know how to add another straight line (grapihcs) on the existing straight line on my left panel. could you help me please?

thank you!

Your doing some basic no-no's in your graphics code such as subclassing paint and paintComponent where only paintComponent is needed, calling setBackground from within a paint/paintComponent method,...

I think that you would benefit greatly by reading the Sun graphics tutorials. Good luck.

The basic idea is to keep the lines in a collection which is a member variable (in class scope) and draw all of the lines on each trip through the paintComponent method.
Another approach is to use a BufferedImage that is the same size as the component. You draw each new line to the image in/via your event code and then simply draw/render the image in the paintComponent method.

Code:

---

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Line2D;
import java.util.*;
import java.util.List;
import javax.swing.*;

public class AddingLines extends JPanel {
    List<Line2D.Double> lines = new ArrayList<Line2D.Double>();
    Random seed = new Random();

    public AddingLines() {
        setBackground(Color.white);
    }

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setPaint(Color.blue);
        for(int i = 0; i < lines.size(); i++) {
            g2.draw(lines.get(i));
        }
    }

    private void addLine() {
        int w = getWidth();
        int h = getHeight();
        int x1 = seed.nextInt(w);
        int y1 = seed.nextInt(h);
        int x2 = seed.nextInt(w);
        int y2 = seed.nextInt(h);
        lines.add(new Line2D.Double(x1, y1, x2, y2));
        repaint();
    }

    private JPanel getLast() {
        JButton button = new JButton("add line");
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                addLine();
            }
        });
        JPanel panel = new JPanel();
        panel.add(button);
        return panel;
    }

    public static void main(String[] args) {
        AddingLines test = new AddingLines();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(test);
        f.add(test.getLast(), "Last");
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
}

---

It's funny. Our apps were a bit similar:

Code:

---

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Line2D;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.swing.*;

public class ShowLines
{
  private static final int WIDTH = 400;
  private static final Dimension GP_SIZE = new Dimension(WIDTH, WIDTH);
  private static final String ADD_LINE = "Add Random Line";
  private static final String REMOVE_LINE = "Remove Random Line";
  private static final float STROKE = 6f;
  private JPanel mainPanel = new JPanel();
  private List<Line2D> lineList = new ArrayList<Line2D>();
  private JPanel graphicsPanel = new JPanel()
  {
    protected void paintComponent(Graphics g)
    {
      super.paintComponent(g);
      myPaint(g);
    }
  };

  public ShowLines()
  {
    graphicsPanel.setPreferredSize(GP_SIZE);
    graphicsPanel.setBorder(BorderFactory.createLineBorder(Color.blue, 3));
    JPanel buttonPanel = createButtonPanel();
   
    mainPanel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
    mainPanel.setLayout(new BorderLayout(5, 5));
    mainPanel.add(graphicsPanel, BorderLayout.CENTER);
    mainPanel.add(buttonPanel, BorderLayout.EAST);
  }
 
  private void myPaint(Graphics g)
  {
    Graphics2D g2 = (Graphics2D)g;
    RenderingHints rh = new RenderingHints(
        RenderingHints.KEY_ANTIALIASING,
        RenderingHints.VALUE_ANTIALIAS_ON);
    g2.setRenderingHints(rh);
    g2.setColor(Color.red);
    g2.setStroke(new BasicStroke(STROKE));
    for (Line2D line : lineList)
    {
      g2.draw(line);
    }
  }
 
  private JPanel createButtonPanel()
  {
    JButton addLineBtn = new JButton(ADD_LINE);
    JButton removeLineBtn = new JButton(REMOVE_LINE);
    LineListener lineListener = new LineListener();
    addLineBtn.addActionListener(lineListener);
    removeLineBtn.addActionListener(lineListener);
   
    JPanel innerPanel = new JPanel(new GridLayout(0, 1, 0, 10));
    innerPanel.add(addLineBtn);
    innerPanel.add(removeLineBtn);
   
    JPanel bp = new JPanel();
    bp.add(innerPanel);
    return bp;
  }

  public JComponent getComponent()
  {
    return mainPanel;
  }

  private class LineListener implements ActionListener
  {
    private Random random = new Random();
   
    public void actionPerformed(ActionEvent e)
    {
      String actionCommand = e.getActionCommand();
      if (actionCommand.equals(ADD_LINE))
      {
        Line2D line = new Line2D.Double(
            random.nextInt(WIDTH),
            random.nextInt(WIDTH),
            random.nextInt(WIDTH),
            random.nextInt(WIDTH)
            );
        lineList.add(line);
      }
      else if (actionCommand.equals(REMOVE_LINE))
      {
        if (lineList.size() > 0)
        {
          lineList.remove(0);
        }
      }
      graphicsPanel.repaint();
    }
  }
  private static void createAndShowUI()
  {
    JFrame frame = new JFrame("ShowLines");
    frame.getContentPane().add(new ShowLines().getComponent());
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }

  public static void main(String[] args)
  {
    java.awt.EventQueue.invokeLater(new Runnable()
    {
      public void run()
      {
        createAndShowUI();
      }
    });
  }
}

---

thanks guys!

by the way, how can i add regular text at the bottom of the last button? say i wanted to type in a few words.

thanks again!