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  1. #1
    cms370 is offline Member
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    Default 2D Graph Repaint Issue

    Hello all...newb question. Please bare with me.

    I am trying to build a simple graph that will plot array values. I would like for this graph to update so that I have a "live" graph.

    I have built something (starting with a very generic 2d graphics example) that will plot one array, wait for 2 seconds, then plot the other array. Everything plots as it should, but the old data remains over top of the new data, until I resize the window. Then everything is as it should be.

    Could someone explain why repaint() does not work? I saw that revalidate() should be used in these situations, but this only applies to JPanels??

    Thanks for the help.

    Here is the code:

    import java.awt.*;
    import javax.swing.*;
    import java.awt.geom.*;

    public class JustaFrame2 extends JFrame {

    public int[] plot_x;
    public int[] plot_y;

    public JustaFrame2(int[] data_x, int[] data_y){
    plot_x = data_x;
    plot_y = data_y;

    public void paint(Graphics g){

    //set preliminary
    setDefaultCloseOperation(javax.swing.WindowConstan ts.EXIT_ON_CLOSE);
    Graphics2D g2 = (Graphics2D) g;
    // fill Ellipse2D.Double

    for(int i=0;i<5;i++) {
    g2.fill (new Ellipse2D.Double(plot_x[i], plot_y[i], 10, 10));


    public static void main(String[] args) throws InterruptedException {

    int[] plot_x = {500,400,300,200,100};
    int[] plot_y = {100,200,300,400,500};
    int[] new_data = {100,200,300,400,500};
    JustaFrame2 frame = new JustaFrame2(plot_x,plot_y);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOS E);
    System.out.println("New Data");
    System.arraycopy(new_data,0,plot_x,0,new_data.leng th);
    System.arraycopy(new_data,0,plot_y,0,new_data.leng th);

  2. #2
    Fubarable's Avatar
    Fubarable is offline Moderator
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    Default Re: 2D Graph Repaint Issue

    Please read a tutorial on drawing in Swing before doing this as you're doing several things wrong, things that a good tutorial would have shown you was wrong early on. For instance, you almost never draw directly in a top level container, but rather in a component derived from JComponent such as a JPanel. Also you should draw in the JPanel's paintComponent method and should call the super's method first in your override, but again, the tutorials will show you all of this.

  3. #3
    DarrylBurke's Avatar
    DarrylBurke is offline Forum Police
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    Default Re: 2D Graph Repaint Issue

    1. Unrelated to the posted problem, but do not set the defaultCloseOperation or otherwise change the state of a component ion a painting method override.
    2. Don't attempt custom painting in a top level window. Learn how to do it correctly here: Lesson: Performing Custom Painting (The Java™ Tutorials > Creating a GUI With JFC/Swing)

    If you're forever cleaning cobwebs, it's time to get rid of the spiders.

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