I have a java program that creates a JFrame like this:
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
gui.setFrame(new gui(), 1000, 300);
}
});
I also have a class (gui.java) that implements setFrame:
public static void setFrame(final JFrame frame, final int width, final int height) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
f1=frame;
frame.setTitle("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(width, height);
frame.setVisible(true);
}
});
}
If the user tries to click Submit (a button I created) and the fields in the JFrame are not filled in then it throws an error. The code for the error message is:
submit.addMouseListener(new MouseListener(){
#Override
public void mouseClicked(MouseEvent e) {}
#Override
public void mouseEntered(MouseEvent e) {}
#Override
public void mouseExited(MouseEvent e) {}
#Override
public void mousePressed(MouseEvent e) {}
#Override
public void mouseReleased(MouseEvent e) {
//check to make sure all values filled in
if(chooser.getSelectedFile().toString()!=null&&saveChooser.getSelectedFile().toString()!=null)
parseFile.readFile(chooser.getSelectedFile(),saveChooser.getSelectedFile(),startSpanText.getText(),(String)col2.getSelectedItem(),(String)col3.getSelectedItem(),(String)col4.getSelectedItem(),(String)col5.getSelectedItem(),(String)col6.getSelectedItem());
else
JOptionPane.showMessageDialog(f1,"Bad");
}
});
//Note: f1 is a static version of the frame I initially received
The error I get is:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at gui$3.mouseReleased(gui.java:133)
at java.awt.AWTEventMulticaster.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(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)
What did I do wrong?
One of the variables is null. It could be:
chooser
chooser.getSelectedFile()
saveChooser
saveChooser.getSelectedFile()
parseFile
startSpanText
col2 to col6
Use the line number in the stack trace, and a debugger or traces in the code to know which one. My guess would be one of the selected files, since it makes no sense to call
chooser.getSelectedFile().toString() != null
Either there is no selected file, and it throws an NPE because getSelectedFile() returns null, or there is one, and its toString() will never be null.
Also, you shouldn't use a mouse listener to do something when a button is pressed. That's what an ActionListener is for. It will be simpler, and also work when the user presses the button with its keyboard.
Your exception message should point you to the answer. One of the items you are using in your mouseReleased method is null:
#Override
public void mouseReleased(MouseEvent e) {
//check to make sure all values filled in
if(chooser.getSelectedFile().toString()!=null &&
saveChooser.getSelectedFile().toString()!=null)
parseFile.readFile(chooser.getSelectedFile(), saveChooser.getSelectedFile(),
startSpanText.getText(), (String)col2.getSelectedItem(),
(String)col3.getSelectedItem(), (String)col4.getSelectedItem(),
(String)col5.getSelectedItem(), (String)col6.getSelectedItem());
else
JOptionPane.showMessageDialog(f1,"Bad");
}
Use a debugger to inspect which variables are set. Use the line number in the exception message to help you.
Related
As a follow-up to this question that I posted earlier, I am wondering about the cause of the issue I had.
The problem was that I was getting this error when updating a JLabel with a lot of HTML text.
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.text.html.StyleSheet$ListPainter.paint(Unknown Source)
at javax.swing.text.html.ListView.paintChild(Unknown Source)
at javax.swing.text.BoxView.paint(Unknown Source)
at javax.swing.text.html.BlockView.paint(Unknown Source)
at javax.swing.text.html.ListView.paint(Unknown Source)
at javax.swing.text.BoxView.paintChild(Unknown Source)
at javax.swing.text.BoxView.paint(Unknown Source)
at javax.swing.text.html.BlockView.paint(Unknown Source)
at javax.swing.text.BoxView.paintChild(Unknown Source)
at javax.swing.text.BoxView.paint(Unknown Source)
at javax.swing.text.html.BlockView.paint(Unknown Source)
at javax.swing.text.BoxView.paintChild(Unknown Source)
at javax.swing.text.BoxView.paint(Unknown Source)
at javax.swing.text.html.BlockView.paint(Unknown Source)
at javax.swing.plaf.basic.BasicHTML$Renderer.paint(Unknown Source)
at javax.swing.plaf.basic.BasicLabelUI.paint(Unknown Source)
at javax.swing.plaf.ComponentUI.update(Unknown Source)
at javax.swing.JComponent.paintComponent(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintToOffscreen(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
at javax.swing.RepaintManager.paint(Unknown Source)
at javax.swing.JComponent._paintImmediately(Unknown Source)
at javax.swing.JComponent.paintImmediately(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.access$1200(Unknown Source)
at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(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)
The HTML that's being set is generated by a StringBuilder and the converted .toString. Something like this, but more extensive:
public static String entityOverviewHTML() {
StringBuilder sb = new StringBuilder();
List<Entity> entities = Entity.getEntities();
sb.append("<html><div style='padding: 12px;'>");
sb.append("<h1>People: alive</h1>");
// A lot of appending: also loop through getEntities (dynamic, can change)
// and get contents from each entity in #getEntityInfo below
if (entities.size() > 0) {
sb.append("<ul>");
for (Entity e: entities) {
getEntityInfo(e);
}
sb.append("</ul>");
}
sb.append("</div></html>");
return sb.toString();
}
private static StringBuilder getEntityInfo(Entity e) {
StringBuilder sbInfo = new StringBuilder();
// A lot of appending: append info of Entity e such as e.getFirstName()
sbInfo.append("<li>");
sbInfo.append(e.getFirstName())
sbInfo.append("</li>");
return sbInfo;
}
After some events, the HTML will change after which I call a custom refresh method:
public static void bringToFront() {
getInstance().setVisible(true);
getInstance().setExtendedState(JFrame.ICONIFIED);
getInstance().setExtendedState(JFrame.NORMAL);
}
public static void refresh() {
// text is a JLabel
text.setText(entityOverviewHTML());
bringToFront();
}
And it's then that the errors at the top of this post happen, however not always! I haven't figured out why this happens, but I did find that when resetting the text to an empty string and then calling entityOverviewHTML solves the issue.
public static void refresh() {
text.setText(""); // Here we go
text.setText(entityOverviewHTML());
bringToFront();
}
text is defined as a Class variable:
private static JLabel text = new JLabel();
What I like to know is: why? How can this single line of seemingly obsolete code solve the problem? Exactly what is the problem?
The problem is that your refresh() method is not called on the Swing EDT.
Swing is not threadsafe (https://docs.oracle.com/javase/tutorial/uiswing/concurrency/dispatch.html) which means that the call text.setText(entityOverviewHTML()); corrupts the internal data structures that your JLabel instance uses to display the text.
Your refresh-method needs to be rewritten like this:
public static void refresh() {
try {
SwingUtilities.invokeAndWait(new Runnable() {
public void run() {
text.setText(entityOverviewHTML());
bringToFront();
}
});
} catch (InvocationTargetException | InterruptedException e) {
e.printStackTrace();
}
}
Usually when JLabel is instantiated, it has no width , if it is instantiated with empty text width is zero. When JLabel text is updated it won't show up as its size is not set properly.
Use preferred size: text.setPreferredSize(new Dimension(x, y)); then text.setText(html)
I'm new to programming and I was making a calculator with only 1 textfield.
I need a method which can recognize which string characters from these (+ , - , * , /)
to send the result to a variable and when i click the = button it shows the result.
I have tried to write something like that (1+2) and save it to variable then then when I try to press = button to settext the variable it shows a privilage error.
Here is the code
JButton btnOne = new JButton("1");
btnOne.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
sum+=1;
txtoprtn.setText(txtoprtn.getText()+"1");
JButton btnTwo = new JButton("2");
btnTwo.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
sum+=2;
txtoprtn.setText(txtoprtn.getText()+"2");
}
});
JButton btnAdd = new JButton("+");
btnAdd.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
txtoprtn.setText(txtoprtn.getText()+"+");
}
});
JButton btnEqual = new JButton("=");
btnEqual.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
x = Integer.parseInt(txtoprtn.getText());
txtoprtn.setText(Integer.toString(x));
}
}
);
and this is the error
**Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: "1+2"
at java.lang.NumberFormatException.forInputString(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at com.jadv.day01.tasks.AdvCalc$11.actionPerformed(AdvCalc.java:140)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(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)**
any suggestions????
First problem
When you try to just write a string statement of "1+2", what do you expect will happen? It can't simply just be evaluated like that. You would have to first use Integer.parseInt() to each of your # buttons after the number insertion is done(say, when you click the +/-///*, or =. That means the number is done and you'll get say
Integer.parseInt("123") instead of Integer.parseInt("1")+Integer.parseInt("2")+Integer.parseInt("3")
What you're trying to do is parsing a + in the middle of the parse. Keep the integer parse to the numbers and the operators stored somewhere else(explained in second problem)
Second problem
When you say "+", that doesn't parse into any operation. You would have to store the values into their individual variables and when clicked a + button, you would get a correct answer. If you want to do this without any external imports, then you would have to store the operations in a list and evaluate when = is clicked.
btnAdd.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
operations.add("+");//operations is a list
}
});
Solving both problems at once using an import
If you want to evaluate using a package, then use this:
ScriptEngine evaluationMachine = new ScriptEngineManager().getEngineByName("JavaScript");
engine.eval(foo); //evaluates something like "2+1" into 3.
with the following imports:
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
EDIT: By the way, though the second way is much faster, you should probably try and write it without external imports since you're new to programming. There will be inevitable situations where you're going to have to think about the problem.
The cause of the exception is that you are trying to parse a String like "1+2" to an Integer in the line:
x = Integer.parseInt(txtoprtn.getText());
You should store the numbers somewhere else, i.e. in an ArrayList.
I'm writing a code that involves JFrame, and a thread.
The thread should take the text from a text field and write it into text area.
I have 4 buttons as follows:
"Start" to start the thread.
"Stop" which stops the thread.
"Pause" which pause and continues the thread.
and "Exit" which stops the thread and exits the program.
I've created the thread and implemented "run()" function in frame's constructor, here it is:
WritingThread = new Thread(new Runnable() {
#Override
public void run() {
String s = WrittenText.getText();
while(true)
{
for(int i = 0; i < 4; i++)
{
for(int j = 0; j < s.length(); j++)
{
WritingArea.append("" + s.charAt(j));
try {
Thread.sleep((int)ThreadSpeedSpinner.getValue());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
WritingArea.append("\n");
}
WritingArea.setText("");
}
}
});
and these are the buttons:
JButton btnStart = new JButton("Start");
btnStart.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
if(!WritingThread.isAlive())
WritingThread.start();
}
});
JButton btnStop = new JButton("Stop");
btnStop.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
if(WritingThread.isAlive())
WritingThread.stop();
}
});
btnPause = new JButton("Pause");
btnPause.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
if(!isPaused)
{
if(WritingThread.isAlive())
{
WritingThread.suspend();
btnPause.setText("Continue");
isPaused = true;
}
}
else
{
WritingThread.resume();
btnPause.setText("Pause");
}
}
});
JButton btnExit = new JButton("Exit");
btnExit.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
WritingThread.stop();
System.exit(0);
}
});
I have two problems showing up:
When I use stop(), suspend(), or resume(), I get a warning says "The method from the type Thread is deprecated".
When I run the program, I start the thread, then stop it, then try to start it I have this exception
Exception in thread "AWT-EventQueue-0" java.lang.IllegalThreadStateException
at java.lang.Thread.start(Unknown Source)
at com.HomeWork.HomeWork5$6.actionPerformed(HomeWork5.java:140)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(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)
I don't want direct answers, I want to understand why I'm getting these errors, and if there any resources I should go through.
P.S. I searched for an answer a lot and didn't get anything explaining this problem.
Thanks
Threads acquire lock on objects. And the most important part of multithreading
is to safely interweave the threads, so that all the threads can use the resource (object).
If not dealt with correctly, it leads to deadlock.
When you use stop(), you are killing the thread. That thread is gone forever. It
may lead the objects, that stopped thread had acquired, in a inconsistent state.
suspend() is deprecated, because once the thread is suspended other threads won't get the
resource, since the suspended thread holds a lock on it.
The image below describes how threads should be correctly used.
Use sleep(), wait(), and notify() for interleaving the threads efficiently.
today I'm having a bit of a slight, see, I'm trying to run my code and I'm getting a NullPointerException. The clues in the exception leads me to this function right here:
private void irGuiJuego(JFrame frame){
SwingConsole.run(new GUIJuego(), 800, 600, true);
frame.dispose();
}
Where SwingConsole would have this code:
package utiles;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
public class SwingConsole {
public static void run(final JFrame frame, final int width, final int height, final boolean exitOnClose) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
if (exitOnClose)
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(width, height);
//frame.setResizable(false);
frame.setVisible(true);
}
});
}
public static void run(final JFrame frame, final int width, final int height, final boolean exitOnClose, final String title) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
if (exitOnClose)
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setTitle(title);
frame.setSize(width, height);
frame.setVisible(true);
}
});
}
}
It is kind of odd, considering that I'm using the same method to open up another frame, in this function to be specific:
private void volverMenuInicio(JFrame frame){
SwingConsole.run(new MenuInicio(), 300, 150, true);
frame.dispose();
}
I'll leave you guys a pastebin of the GUIJuego Frame, since it's sort of excessive to post it here: http://pastebin.com/LSXbc7KE , have the pastebin of the other frame too, in case you need it: http://pastebin.com/hbdd7j84
Edit: Here's the stacktrace, sorry for the lack of it before!
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.awt.Container.addImpl(Unknown Source) at
java.awt.Container.add(Unknown Source) at
gui.GUIJuego.(GUIJuego.java:113) at
gui.MenuNuevoJuego.irGuiJuego(MenuNuevoJuego.java:95) at
gui.MenuNuevoJuego.access$2(MenuNuevoJuego.java:94) at
gui.MenuNuevoJuego$2.actionPerformed(MenuNuevoJuego.java:74) at
javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at
javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at
javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at
javax.swing.DefaultButtonModel.setPressed(Unknown Source) at
javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown
Source) at java.awt.Component.processMouseEvent(Unknown Source) at
javax.swing.JComponent.processMouseEvent(Unknown Source) at
java.awt.Component.processEvent(Unknown Source) at
java.awt.Container.processEvent(Unknown Source) at
java.awt.Component.dispatchEventImpl(Unknown Source) at
java.awt.Container.dispatchEventImpl(Unknown Source) at
java.awt.Component.dispatchEvent(Unknown Source) at
java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) at
java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) at
java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) at
java.awt.Container.dispatchEventImpl(Unknown Source) at
java.awt.Window.dispatchEventImpl(Unknown Source) at
java.awt.Component.dispatchEvent(Unknown Source) at
java.awt.EventQueue.dispatchEventImpl(Unknown Source) at
java.awt.EventQueue.access$200(Unknown Source) at
java.awt.EventQueue$3.run(Unknown Source) at
java.awt.EventQueue$3.run(Unknown Source) at
java.security.AccessController.doPrivileged(Native Method) at
java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown
Source) at
java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown
Source) at java.awt.EventQueue$4.run(Unknown Source) at
java.awt.EventQueue$4.run(Unknown Source) at
java.security.AccessController.doPrivileged(Native Method) at
java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown
Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at
java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(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 reading, by the way!
The NPE is being thrown from line 113 in GUIJuego.java, as the stack trace indicates:
panelDatosCiudad.add(arcaLabel);
It's happening because arcaLabel, defined in line 35, is never set to a value, and so you're adding a null JLabel to the container.
I am trying to design a three cascade JComboBox in JAVA:
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.WindowConstants;
public class ThreeCascadeJComboBox {
private JComboBox combo1;
private JComboBox combo2;
private JComboBox combo3;
public static void main(String[] args) {
new ThreeCascadeJComboBox();
}
public ThreeCascadeJComboBox() {
JFrame v = new JFrame();
v.getContentPane().setLayout(new FlowLayout());
combo1 = new JComboBox();
loadCombo1();
combo1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
loadCombo2((String) combo1.getSelectedItem());
}
});
combo2 = new JComboBox();
loadCombo2((String) combo1.getSelectedItem());
combo2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
loadCombo3((String) combo2.getSelectedItem());
}
});
combo3 = new JComboBox();
loadCombo3((String) combo2.getSelectedItem());
v.getContentPane().add(combo1);
v.getContentPane().add(combo2);
v.getContentPane().add(combo3);
v.pack();
v.setVisible(true);
v.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
}
private void loadCombo1() {
combo1.addItem("letters");
combo1.addItem("numbers");
}
private void loadCombo2(String seleccionEnCombo1) {
combo2.removeAllItems();
if (seleccionEnCombo1.equals("letters")) {
combo2.addItem("A");
combo2.addItem("B");
combo2.addItem("C");
} else if (seleccionEnCombo1.equals("numbers")) {
combo2.addItem("1");
combo2.addItem("2");
combo2.addItem("3");
}
}
private void loadCombo3(String seleccionEnCombo2) {
combo3.removeAllItems();
if (seleccionEnCombo2.equals("A")) {
combo3.addItem("A-1");
combo3.addItem("A-2");
combo3.addItem("A-3");
} else if (seleccionEnCombo2.equals("B")) {
combo3.addItem("B-1");
combo3.addItem("B-2");
combo3.addItem("B-3");
} else if (seleccionEnCombo2.equals("C")) {
combo3.addItem("C-1");
combo3.addItem("C-2");
combo3.addItem("C-3");
} else if (seleccionEnCombo2.equals("1")) {
combo3.addItem("1-a");
combo3.addItem("1-b");
combo3.addItem("1-c");
} else if (seleccionEnCombo2.equals("2")) {
combo3.addItem("2-a");
combo3.addItem("2-b");
combo3.addItem("2-c");
} else if (seleccionEnCombo2.equals("3")) {
combo3.addItem("3-a");
combo3.addItem("3-b");
combo3.addItem("3-c");
}
}
}
But I get the next Exception when I select the numbers value in the jcombo1:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at es.mycompany.MyView.ThreeCascadeJComboBox.loadCombo3(ThreeCascadeJComboBox.java:78)
at es.mycompany.MyView.ThreeCascadeJComboBox.access$3(ThreeCascadeJComboBox.java:76)
at es.mycompany.MyView.ThreeCascadeJComboBox$2.actionPerformed(ThreeCascadeJComboBox.java:40)
at javax.swing.JComboBox.fireActionEvent(Unknown Source)
at javax.swing.JComboBox.contentsChanged(Unknown Source)
at javax.swing.JComboBox.intervalRemoved(Unknown Source)
at javax.swing.AbstractListModel.fireIntervalRemoved(Unknown Source)
at javax.swing.DefaultComboBoxModel.removeAllElements(Unknown Source)
at javax.swing.JComboBox.removeAllItems(Unknown Source)
at es.mycompany.MyView.ThreeCascadeJComboBox.loadCombo2(ThreeCascadeJComboBox.java:63)
at es.mycompany.MyView.ThreeCascadeJComboBox.access$1(ThreeCascadeJComboBox.java:62)
at es.mycompany.MyView.ThreeCascadeJComboBox$1.actionPerformed(ThreeCascadeJComboBox.java:30)
at javax.swing.JComboBox.fireActionEvent(Unknown Source)
at javax.swing.JComboBox.setSelectedItem(Unknown Source)
at javax.swing.JComboBox.setSelectedIndex(Unknown Source)
at javax.swing.plaf.basic.BasicComboPopup$Handler.mouseReleased(Unknown Source)
at java.awt.AWTEventMulticaster.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at javax.swing.plaf.basic.BasicComboPopup$1.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$400(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(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)
The exception is thrown because at that point seleccionEnCombo2 is null.
You could add a check for null in the combo2 ActionListener and it will work fine:
if (combo2.getSelectedItem() != null) {
loadCombo3((String) combo2.getSelectedItem());
}
The problem is that the ActionListener for combo1 is triggering an ActionEvent for combo2 which will not have any selected item (as it is empty). You could add a check:
if (combo2.getSelectedItem() != null) {
loadCombo3((String) combo2.getSelectedItem());
}
As the other posts have mentioned, the selected value for the combo is null in some cases. This is occurring because you probably do not realize the ActionListener for combo2 is getting called twice. The first time it gets called is during the call to removeAllElements. This is where the null value is coming from. The second time is what you are assuming in your code to be the only call--this is in response to both population of the combo box as well as user interaction.
When you load the second combo box, that fires the action event for that box (because an action has taken place [actions are not limited to selection]. The 2nd combo box's actionPerformed attempts to load the 3rd combo box based on the 2nd combo box's selection, and there isn't any. That's your null pointer, the non-existent selection from the second combo box.