How to: clear the JPanel before repainting?

[Aji Prasetyo]

Hi all,

I want to plot the data into JPanel periodically. But the problem is everytime the new data gets plotted, the last time plotted data remains drawn in the JPanel. Resulting an overlaped plotted data.
My question is how do you clear the JPanel before repainting?

Thank you so much.

This is the code I am talking about:

package test1;
 
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.lang.reflect.InvocationTargetException;
import java.util.Scanner;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
 
public class TestMouseListener extends javax.swing.JApplet {
    
    public void init() {
        try {
            java.awt.EventQueue.invokeAndWait(new Runnable() {
                public void run() {
                    initComponents();
                }
            });
        } catch(InvocationTargetException ex) { ex.printStackTrace();
        } catch(InterruptedException ex) { ex.printStackTrace(); }
    }
    
    public void start() {
        
        new Thread(new DataCreator()).start();
    }
    
    // <editor-fold defaultstate="collapsed" desc=" Generated Code">                          
    private void initComponents() {
        jPanel1 = new PanelView();
 
        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 376, Short.MAX_VALUE)
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 280, Short.MAX_VALUE)
        );
 
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addContainerGap())
        );
    }// </editor-fold>                        
    
    // Variables declaration - do not modify                     
    private javax.swing.JPanel jPanel1;
    // End of variables declaration                   
}
 
/*----------------------------------------------------------------------------*/
 
class PanelView extends JPanel implements Runnable {
    
    public PanelView() {
        
        new Thread(this).start();
    }
    
    public void paintComponent(Graphics g) {
        
        Dimension d = getSize();
        int xmax = d.width - 1;
        int ymax = d.height - 1;
        int xcntr = xmax / 2;
        int ycntr = ymax / 2;
        java.util.List<java.awt.Point> dataPoints = new ScanDataPool().readData();
        setBackground(Color.WHITE);
        for(int i = 0; i < dataPoints.size(); i++) {
            g.drawOval((dataPoints.get(i).x / 6) + xcntr, (dataPoints.get(i).y / 6) + ycntr, 1, 1);
        }
    }
    
    public void run() {
        
        for(int i = 0; i < 10; i++) {
            System.out.println("PanelView " + i + " times...");
            try {
                Thread.currentThread().sleep(1000);
                SwingUtilities.invokeLater(new Runnable() {
                    public void run() {
                        PanelView.this.repaint();
                    }
                });
            } catch(InterruptedException ex) { ex.printStackTrace(); }
        }
        System.out.println("PanelView thread is over...");
    }
}
 
/*----------------------------------------------------------------------------*/
 
class ScanDataPool {
    
    private File ffile = new File("TestMouseListener.txt");
    
    public synchronized java.util.List<java.awt.Point> readData() {
        
        Scanner inStream = null;
        java.util.List<java.awt.Point> dataPoints = new java.util.ArrayList<java.awt.Point>();
        
        if(ffile.exists()) {
            try {
                inStream = new Scanner(new BufferedReader(new FileReader(ffile)));
                inStream.useDelimiter("\\s*[xy\n]\\s*");
                dataPoints.clear();
                for(int i = 0; i < 681; i++) {
                    if(i == inStream.nextInt()) {
                        dataPoints.add(new java.awt.Point(inStream.nextInt(), inStream.nextInt()));
                    }
                }
            } catch(FileNotFoundException ex) { ex.printStackTrace();
            } finally { if(inStream != null) inStream.close(); }
        } else {
            System.out.println("TestMouseListener.txt is not exists while readData()...");
            System.exit(0);
        }
        return dataPoints;
    }
    
    public synchronized void writeData(java.util.List<java.awt.Point> dataPoints) {
        
        PrintWriter outStream = null;
        
        if(dataPoints != null) {
            try {
                outStream = new PrintWriter(new BufferedWriter(new FileWriter(ffile)));
                for(int i = 0; i < dataPoints.size(); i++) {
                    outStream.println(i + " x " + dataPoints.get(i).x + " y " + dataPoints.get(i).y);
                }
                outStream.flush();
            } catch(IOException ex) { ex.printStackTrace();
            } finally { if(outStream != null) outStream.close(); }
        } else {
            System.out.println("dataPoints is NULL while writeData()...");
            System.exit(0);
        }
    }
}
 
/*----------------------------------------------------------------------------*/
 
class DataCreator implements Runnable{
    
    public void run() {
        
        java.util.List<java.awt.Point> dataPoints = new java.util.ArrayList<java.awt.Point>();
        
        for(int i = 1; i < 10; i++) {
            System.out.println("DataCreator " + i + " times...");
            try {
                Thread.currentThread().sleep(1000);
                int rdius = i * 250;
                dataPoints.clear();
                for(int n = 0; n < 681; n++) {
                    double ALPH = (double)(n * (2 * Math.PI / 680)) + (Math.PI / 2);
                    int xCor = (int)((double)rdius * Math.cos(ALPH));
                    int yCor = (int)((double)rdius * Math.sin(ALPH));
                    dataPoints.add(new java.awt.Point(xCor, yCor));
                }
                new ScanDataPool().writeData(dataPoints);
            } catch(InterruptedException ex) { ex.printStackTrace(); }
        }
        System.out.println("DataCreator thread is over...");
    }
}

[Nacho Espinosa]

For clear JPanel this is my suggest.

JPanel panel = new JPanel();
//remove all components in panel.
panel.removeAll();
// refresh the panel.
panel.updateUI();

[Campbell Ritchie]

The first line of your paintComponent method should read

super.paintComponent(g);

[Aji Prasetyo]

Hi,

I put

super.paintComponent(g);

at the first line of my

paintComponent()

and it works.

Thank you guys.

[Campbell Ritchie]

You're welcome. Only too pleased to help. The statement super.paintComponent(g) seems to return the JPanel or whatever to its original state, then you can draw whatever you want on it.

[carol sa]

Nacho Espinosa ,

while hunting for solution for my problem updating my Jpanel, I found you suggestion.... you made my day with your code suggestion, my problem solved in a second

[Campbell Ritchie]

carol sa wrote:Nacho Espinosa ,

while hunting for solution for my problem updating my Jpanel, I found you suggestion.... . . .

I hope you aren't using that suggestion while repainting. It is very inefficient to remove and re-create all your components.

For repainting, super.paintComponent(g);

If you need to repopulate your panel, then the remove methods are useful. But why would you wish to change the displayed components?