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JTabel: setting a new value; setValueAt; NullPointerException

Hi,

I had already a similar problem, this time I have to ask this forum again:

I have a GUI with some JPanels laid out using BorderLayout. One of these JPanels contains my JTable; this JPanel is in a separate class.

In another class some methods calculate speed, angle, distance etc... values I need for my program.

I just want to enter these calculated values in my JTable so that the user can see them. So, the JTable itself should just show the values. I don't want that the user can change the values or that the table respond to events.

Here is my class "InfoPanel" which contains the JTable:

publicclass InfoPanelextends JComponent{

privatestaticfinallong serialVersionUID = 1;

public JTable table;

String[] columnNames ={"Type","Value"};

Object[][] rowData ={

"Angle","0"},

};

public InfoPanel(){

setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));

Dimension dim_wPanel =new Dimension(300, 150);

JPanel wPanel =new JPanel();

wPanel.setPreferredSize(dim_wPanel);

table =new JTable(rowData, columnNames);

table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);

JPanel tablePanel =new JPanel();

tablePanel.setLayout(new BorderLayout());

tablePanel.add(table.getTableHeader(), BorderLayout.PAGE_START);

tablePanel.add(table, BorderLayout.CENTER);

add(windDirectionPanel);

add(tablePanel);

}

}

...and here is my class calculating some values and using the setValueAt method (just including the necessary code):

publicclass PlayerMgmtextends JComponent{

privatestaticfinallong serialVersionUID = 1;

InfoPanel ip;

private List <Ellipse2D>playerList =new ArrayList<Ellipse2D>();

public PlayerMgmt(){

(...)

}

protectedvoid paintComponent(Graphics g){

(...)

if (pList.size() > 1){

ip.table.getModel().setValueAt(calcAngle(player, playerLast), 0, 1);

}

}

(...)

private String calcAngle(Ellipse2D p, Ellipse2D lp){

double radians = (Math.atan2(lp.getY() - p.getY(), lp.getX() - p.getX()) * 180.0) / Math.PI;

return formatter.format(radians);

}

}

The setValueAt method results in a NullPointerException:

Exception in thread"AWT-EventQueue-0" java.lang.NullPointerException

What am I doing wrong?

Thanks for your help!

[4116 byte] By [SFLa] at [2007-11-26 16:48:51]
«« Regular Expression Help
»» class version problem
# 1
The setValueAt method results in a NullPointerException:Exception in thread "AWT-EventQueue-0" java.lang.NullPointerExceptionWhat was wrong with posting the useful part of that exception? ie the stack trace
itchyscratchya at 2007-7-8 23:16:24 > top of Java-index,Desktop,Core GUI APIs...
# 2
You didn't post all the relevant code.But anyway it's a bad idea to setValueAt inside paintComponent which is called every time a repaint is needed.
Rodney_McKaya at 2007-7-8 23:16:24 > top of Java-index,Desktop,Core GUI APIs...
# 3

Oh, here is the full code of the class PlayerMgmt:

import java.awt.Color;

import java.awt.Graphics;

import java.awt.Graphics2D;

import java.awt.Rectangle;

import java.awt.event.MouseAdapter;

import java.awt.event.MouseEvent;

import java.awt.geom.Ellipse2D;

import java.awt.geom.Line2D;

import java.text.DecimalFormat;

import java.text.NumberFormat;

import java.util.ArrayList;

import java.util.List;

import javax.swing.JComponent;

import javax.swing.SwingUtilities;

public class PlayerMgmt extends JComponent {

private static final long serialVersionUID = 1;

private BShapes cb = new BShapes();

private InfoPanel ip;

private List <Ellipse2D>playerList = new ArrayList<Ellipse2D>();

private Ellipse2D player, playerLast;

private Line2D connectingLine;

private NumberFormat formatter = new DecimalFormat("#,###,###");

public PlayerMgmt () {

addMouseListener(new MouseAdapter(){

public void mouseClicked(MouseEvent evt) {

if (SwingUtilities.isLeftMouseButton(evt)) {

playerList.add(new Ellipse2D.Double(evt.getX(), evt.getY(), 20, 20));

}

if (SwingUtilities.isRightMouseButton(evt)) {

if (playerList.size() > 0) playerList.remove(playerList.size() - 1);

}

repaint();

}

});

}

protected void paintComponent(Graphics g) {

super.paintComponent(g);

Graphics2D g2 = (Graphics2D) g;

Rectangle drawHere = g.getClipBounds();

g2.setColor(Color.WHITE);

g2.fillRect(drawHere.x, drawHere.y, drawHere.width, drawHere.height);

g2.setColor(Color.BLACK);

g2.draw(cb.drawIsland());

for(int i=1 ; i < playerList.size(); i++) {

player = playerList.get(i);

playerLast = playerList.get(i-1);

connectingLine = new Line2D.Double(playerLast.getX(), playerLast.getY(), player.getX(), player.getY());

if (isCollision(player, connectingLine)) g2.setColor(Color.RED);

else g2.setColor(Color.BLACK);

g2.draw(player);

g2.draw(connectingLine);

}

// setValueAt

if (playerList.size() > 1) {

ip.table.getModel().setValueAt(calcAngle(player, playerLast), 0, 1);

}

}

private boolean isCollision(Ellipse2D p, Line2D l) {

if (cb.drawRoundedIsland().getBounds().contains(p.getBounds()) || (cb.drawRoundedIsland().getBounds().intersects(l.getBounds()))) return true;

else return false;

}

private String calcAngle(Ellipse2D p, Ellipse2D lp) {

double radians = (Math.atan2(lp.getY() - p.getY(), lp.getX() - p.getX()) * 180.0) / Math.PI;

return formatter.format(radians);

}

}

...and the exception:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

at PlayerMgmt.paintComponent(PlayerMgmt.java:72)

at javax.swing.JComponent.paint(Unknown Source)

at javax.swing.JComponent.paintChildren(Unknown Source)

at javax.swing.JComponent.paint(Unknown Source)

at javax.swing.JComponent.paintWithOffscreenBuffer(Unknown Source)

at javax.swing.JComponent.paintDoubleBuffered(Unknown Source)

at javax.swing.JComponent._paintImmediately(Unknown Source)

at javax.swing.JComponent.paintImmediately(Unknown Source)

at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)

at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(Unknown Source)

at java.awt.event.InvocationEvent.dispatch(Unknown Source)

at java.awt.EventQueue.dispatchEvent(Unknown Source)

at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.run(Unknown Source)

Thanks for your help!

SFLa at 2007-7-8 23:16:24 > top of Java-index,Desktop,Core GUI APIs...
# 4
ip is null because you only define it private InfoPanel ip;But you never initialize it.And anyway like I told your in my previous reply it's a bad idea to setValueAt in the paintComponent function.
Rodney_McKaya at 2007-7-8 23:16:24 > top of Java-index,Desktop,Core GUI APIs...
# 5
Rodney_McKay, thanks for your fast reply! How can I correctly initialize ip? Yes, I will move the setValueAt method out of paintComponent.Thanks!
SFLa at 2007-7-8 23:16:24 > top of Java-index,Desktop,Core GUI APIs...
# 6

You need to supply your InfoPanel object to the contructor of PlayerMgmt and do something like this:

public PlayerMgmt(InfoPanel ip) {

this.ip = ip;

}

This is of course assuming that you create this object somewhere...

Rodney_McKaya at 2007-7-8 23:16:24 > top of Java-index,Desktop,Core GUI APIs...
# 7

I corrected my code but I get a NullPointerException again (caused by setValueAt):

In my main-class I call PlayerMgmt: pmPanel = new PlayerMgmt(ip);

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

at PlayerMgmt.paintComponent(PlayerMgmt.java:73)

at javax.swing.JComponent.paint(Unknown Source)

at javax.swing.JComponent.paintChildren(Unknown Source)

at javax.swing.JComponent.paint(Unknown Source)

at javax.swing.JComponent.paintWithOffscreenBuffer(Unknown Source)

at javax.swing.JComponent.paintDoubleBuffered(Unknown Source)

at javax.swing.JComponent._paintImmediately(Unknown Source)

at javax.swing.JComponent.paintImmediately(Unknown Source)

at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)

at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(Unknown Source)

at java.awt.event.InvocationEvent.dispatch(Unknown Source)

at java.awt.EventQueue.dispatchEvent(Unknown Source)

at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.run(Unknown Source)

SFLa at 2007-7-8 23:16:24 > top of Java-index,Desktop,Core GUI APIs...
# 8
Do you create an instance of InfoPanel ?InfoPanel ip = new InfoPanel();// if the constructor does not need argumentspmPanel = new PlayerMgmt(ip);
ProZa at 2007-7-8 23:16:24 > top of Java-index,Desktop,Core GUI APIs...
# 9
> Do you create an instance of InfoPanel ?This was my mistake :) I did create an instance - but spuriously after I created an instance of PlayerMgmt. A newbie mistake ;)Thanks a lot for your help!
SFLa at 2007-7-8 23:16:24 > top of Java-index,Desktop,Core GUI APIs...
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