Develop Reference

Is there a better way to have JPanels communicate?

I'm working on a game which consists entirely of menus/screens which you interact with using buttons, essentially a text-based game but without the typing. To do this I have been working with Swing to create a basic UI, following this video series.
In order to have actions performed in one panel affect the state of another, I have followed the tutorial and created a UIListener interface, which extends EventListener. When a button is pressed in one JPanel, the fireUIEvent method of the panel is called, which in turn calls the sole method of the interface, uiEventOccurred, which is implemented in an anonymous class inside the main JFrame class. Then the JFrame can do whatever it wants with the event, and modify other JPanels it contains accordingly.
For example, I have a panel that represents the town. It has a button you click to travel to the dungeon. When this button is clicked, the town panel is replaced by the dungeon panel, which has a button you can click to return to the town.
I'll post the relevant classes:
the main frame class
public class GameMainFrame extends JFrame{
public JPanel rightPanel;
public GameMainFrame(String title) {
super(title);
/* Setting The Overall Layout */
setLayout(new BorderLayout());
/* Creating Individual UI Panels */
UIPanel uip_town = new Town_UI();
UIPanel uip_dung = new Dungeon_UI();
/* Creating A Nested Panel */
rightPanel = new JPanel();
rightPanel.setLayout(new BorderLayout());
rightPanel.add(uip_text, BorderLayout.WEST);
rightPanel.add(uip_town, BorderLayout.NORTH);
/* Creating A Listener To React To Events From The UI Panels */
uip_town.addUIListener(new UIListener() {
public void uiEventOccurred(UIEvent event) {
System.out.println("event text: " + event.getText());
if (event.getText().equals("goto_dungeon")) {
rightPanel.remove(uip_town);
rightPanel.add(uip_dung, BorderLayout.NORTH);
validate();
} else if (event.getText().equals("goto_town")) {
rightPanel.remove(uip_dung);
rightPanel.add(uip_town, BorderLayout.NORTH);
validate();
}
}
});
/* Adding Panels To The Content Pane Of The Frame */
Container c = getContentPane();
c.add(uip_info, BorderLayout.WEST);
c.add(rightPanel, BorderLayout.CENTER);
}
}
UIPanel class
public class UIPanel extends JPanel {
private EventListenerList listenerList;
public UIPanel() {
listenerList = new EventListenerList();
}
public void fireUIEvent(UIEvent event) {
Object[] listeners = listenerList.getListenerList();
for (int i = 0; i < listeners.length; i += 2) {
if (listeners[i] == UIListener.class) {
((UIListener) listeners[i + 1]).uiEventOccurred(event);
}
}
}
public void addUIListener(UIListener listener) {
listenerList.add(UIListener.class, listener);
}
public void removeUIListener(UIListener listener) {
listenerList.remove(UIListener.class, listener);
}
}
Town_UI class
public class Town_UI extends UIPanel {
public Town_UI() {
Dimension size = getPreferredSize();
size.height = 466;
setPreferredSize(size);
setBorder(BorderFactory.createTitledBorder("Town"));
JButton btn_dungeon_enter = new JButton("Enter the dungeon");
add(btn_dungeon_enter);
btn_dungeon_enter.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
fireUIEvent(new UIEvent(this, "goto_dungeon"));
}
});
}
}
Dungeon_UI class
public class Dungeon_UI extends UIPanel {
public Dungeon_UI() {
Dimension size = getPreferredSize();
size.height = 466;
setPreferredSize(size);
setBorder(BorderFactory.createTitledBorder("Dungeon"));
JButton btn_town_return = new JButton("Return to town");
add(btn_town_return);
btn_town_return.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
fireUIEvent(new UIEvent(this, "goto_town"));
}
});
}
}
UIEvent object
public class UIEvent extends EventObject {
private String text;
public UIEvent(Object source, String text) {
super(source);
this.text = text;
}
public String getText() {
return text;
}
}
UIListener interface
public interface UIListener extends EventListener {
public void uiEventOccurred(UIEvent e);
}
I have two problems with this. Number one, it is currently bugged. When I run the application, the Town_UI panel appears with its button "Enter the dungeon", and upon clicking on it the frame correctly updates, replacing the Town_UI panel with the Dungeon_UI panel. However, clicking on the "Return to town" button on the dungeon panel doesn't do anything. When trying to debug this I found that the cause was in the UIPanel method fireUIEvent. When the "Return to town" button is pressed, this method is correctly called, but when it creates the Object array using getListenerList, the array is empty, so it skips the for-loop and no action is performed. Because I am unfamiliar with ActionEvents and EventListeners in Java, though, I am not sure how to fix this.
My other problem is that all of the behaviors that occur when a button is pressed are handled in the anonymous class in the GameMainFrame class. This means that if I want to have a bunch of different buttons all do different things (which I do plan on implementing), I'll need a whole bunch of conditionals in the anonymous class to determine what button is pressed and perform the corresponding behavior. I feel like it would be a lot cleaner if the button behavior could be implemented in the anonymous ActionListener class of each button, but I'm not sure how I should restructure my code so that I can do this but also allow any action on any panel able modify any other panel.
In the tutorial I watched he claimed that this implementation of EventListeners was what you should do in order to avoid making your code a rat's nest, but it seems like that is where my code is heading if I use this implementation for what I am trying to do.

Adding more mouselisteners to 1 JButton?

Is it possible to add more than 1 mouselistener to a JButton? You know when I click on the button it should change color and text, and do something (e.g system.out.println), and when I click it again it should go back to the previous state, and print something else.
What I've tried:
JButton b = new JButton("First");
b.setBackground(Color.GREEN);
b.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent e)
{
b.setBackground(Color.RED);
b.setText("Second");
System.out.println("You've clicked the button");
}
if(b.getModel.isPressed){
b.setBackground(Color.GREEN);
b.setText("Second");
System.out.println("You're back");
}
The problem is that the button doesn't go back to the previous state with the color (green) and text, and I don't how to handle that.

First of all, you shouldn't be using a MouseListener to do these things, because a better listener, ActionListener, was built specifically to be used with JButtons and similar entities to notify programs that a button has been pressed.
Having said that, sure you can add multiple ActionListeners (or MouseListeners) to a JButton, or you can have an ActionListener change its behaviors depending on the state of the program (usually meaning the values held by fields of the class).
A problem with your code and question is that I don't see when you expect or want the button to change its color back to green. If after a certain period of time, then have your ActionListener start a Swing Timer that changes the button's color back to green after x milliseconds.
Edit: I see, you want to toggle color -- then use a boolean field that you toggle or check the button's current color and base the listener's response based on that color.
example
import java.awt.Color;
import java.awt.Component;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
#SuppressWarnings("serial")
public class ToggleColor extends JPanel {
public ToggleColor() {
JButton button = new JButton(new MyButtonAction());
button.setBackground(Color.GREEN);
add(button);
}
private static void createAndShowGui() {
ToggleColor mainPanel = new ToggleColor();
JFrame frame = new JFrame("ToggleColor");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> createAndShowGui());
}
}
#SuppressWarnings("serial")
class MyButtonAction extends AbstractAction {
// !! parallel arrays being used below -- avoid if possible
private static final String[] TEXT = {"First", "Second", "Third"};
private static final Color[] COLORS = {Color.GREEN, Color.RED, new Color(108, 160, 220)};
private int index = 0;
public MyButtonAction() {
super(TEXT[0]);
}
#Override
public void actionPerformed(ActionEvent e) {
index++;
index %= TEXT.length;
putValue(NAME, TEXT[index]);
Component c = (Component) e.getSource();
c.setBackground(COLORS[index]);
}
}
This uses an AbstractAction class which is like an ActionListener but on "steroids"

You should only register one lister, but that listener will maintain some state regarding the number for mouse clicks. A simple if/else block will change the actions and change the text on the button label.

How to make a class a component in Java Swing?

I am a beginner in Java programming so I do not know if I may be using the correct terms here. Basically, I have an assignment to program a little applet that changes the color of the background to whatever of the 4 color buttons is pressed. I was given a sample code with ActionListener and was told to use MouseListener to implement it.
I was able to successfully program it to work and then the requirements changed. Below is my current code that works (before the requirements changed).
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class ButtonPanel extends JPanel implements MouseListener{
private JButton abutton, bbutton, cbutton, dbutton;
public ButtonPanel(){
abutton = new JButton("Cyan");
bbutton = new JButton("Orange");
cbutton = new JButton("Magenta");
dbutton = new JButton("Yellow");
add(abutton);
add(bbutton);
add(cbutton);
add(dbutton);
/* register the specific event handler into each button */
abutton.addMouseListener(this);
bbutton.addMouseListener(this);
cbutton.addMouseListener(this);
dbutton.addMouseListener(this);
}
/* implementation for the Mouse Event */
public void mouseClicked(MouseEvent evt){
Object source = evt.getSource();
if (source == abutton) setBackground(Color.cyan);
else if (source == bbutton) setBackground(Color.orange);
else if (source == cbutton) setBackground(Color.magenta);
else if (source == dbutton) setBackground(Color.yellow);
repaint();
}
public void mousePressed(MouseEvent evt){
}
public void mouseEntered(MouseEvent evt){
}
public void mouseReleased(MouseEvent evt){
}
public void mouseExited(MouseEvent evt){
}
}
class ButtonFrame extends JFrame{
public ButtonFrame(){
setTitle("Low-level Mouse Event to Set Color");
setSize(50, 50);
addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){ System.exit(0);}
});
Container contentPane = getContentPane();
contentPane.add(new ButtonPanel());
}
}
public class ME_SetColor {
public static void main(String[] args) {
JFrame frame = new ButtonFrame();
frame.pack();
frame.setSize(400, 250);
frame.setVisible(true);
}
}
The new requirement is to exclude extends JPanel and any other extensions for class ButtonPanel. So the modified class has to be
class ButtonPanel implements MouseListener{
private JButton abutton, bbutton, cbutton, dbutton;
Without JPanel, the ButtonPanel class would not be a component and therefore it can not be added to contentPane. Is there another way to make this ButtonPanel a component so it can be added to contentPane? Or is there any other ways to implement this program?

Without JPanel, the ButtonPanel class would not be a component
You could extend JComponent. JComponent is the base class for Swing components. JPanel itself is a simple extension of JComponent (with one minor difference: a JPanel's opaque property is true by default, whereas it's false by default for JComponent).
But if your requirement is to exclude any extensions for ButtonPanel, you're right, you can't actually make it a component that can be added to a container.
However, you could include a component as a field of ButtonPanel:
class ButtonPanel implements ... {
private JPanel panel;
private JButton abutton, bbutton, cbutton, dbutton;
...
public JPanel getPanel() { return panel; }
}
Then in ButtonFrame:
add(new ButtonPanel().getPanel());
You don't need to call getContentPane() and contentPane.add by the way, as a frame's own add methods automatically do this.

JXTitledPanels in a JPanel a user needs to be able to choose one and click a remove button

I have a JPanel with n number of JXTitledPanels. The user should be able to click the JXTitledPanel and hit a remove button to remove it.
My question is how do I know what JXTitlePanel the user has selected.
here is a screen from my program basically I want a user to click "Hospitals", click remove and the Hospitals Table will disappear.

I'd probably add a "remove" control into the right decoration position. This way you could pass a reference to the control of the JXTiltedPane
titledPane.addRightDecoration(new MyRemoveControl(titkedPane));
Or such

#madprogrammer probably has the simplest answer, but if you don't want to change the look of the application, you could combine your button's actionListener with a mouseListener for the panels.
The mouseListener portion saves the last panel clicked, and the actionListener just removes the panel that was registered by the mouseListener.
Here's a quick sample I cooked up - it doesn't use JXTitledPane but that shouldn't matter because they're all in the same hierarchy.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class TempProject extends JFrame{
public TempProject(){
Box mainContent = Box.createVerticalBox();
//Create Button
JButton removePanel = new JButton("RemovePanel");
RemoveListener listener = new RemoveListener(mainContent);
removePanel.addActionListener(listener);
mainContent.add(removePanel);
//Create Panels
mainContent.add(getPanel(Color.red, listener));
mainContent.add(getPanel(Color.orange, listener));
mainContent.add(getPanel(Color.pink, listener));
mainContent.add(getPanel(Color.magenta, listener));
setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
setContentPane(mainContent);
pack();
setVisible(true);
}
public JPanel getPanel(Color color, RemoveListener l){
JPanel result = new JPanel();
result.setBackground(color);
result.add(new JLabel(color.toString()));
result.addMouseListener(l);
return result;
}
public static void main(String args[])
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
new TempProject();
}
});
}
public static class RemoveListener extends MouseAdapter implements ActionListener{
Component lastSelectedComponent = null;
Container master; //The panel containing the ones being listened to
public RemoveListener(Container master){
this.master = master;
}
#Override
public void mouseClicked(MouseEvent arg0) {
lastSelectedComponent = (Component)arg0.getSource();
}
#Override
public void actionPerformed(ActionEvent e) {
if(lastSelectedComponent != null){
master.remove(lastSelectedComponent);
master.repaint();
}
}
}
}

java delete a component

Current I can add a bunch of customed component objects to the JPanel by pressing "add" JButton. I also got a "delete" JButton which I wish to do the opposite of "add".
My intention is that I can select a component with a mouse and click the delete button and pressto!, the component is gone.
I hook a MouseListener to the panel, and use MouseEvent, e.getComponent() to get w/e current component the mouse clicks on. So if it returns a custom component then a variable "private myComponent current" (already set to null) will point to that component. Then I can just click on "delete" button to remove it. An actionListener already added in "delete" button and in the body it calls this.remove(current) (if current is not null).
However, this doesn't work as I can't remove a component! Any pointer?
If there is an elegant way to managing add/remove components please suggest!
public class MainDisplayPanel extends JPanel implements ActionListener, MouseListener{
private JButton newClassButton;
private JButton deleteButton;
private Resizable current;
private Resizable resizer;
public MainDisplayPanel(LayoutManager layout) {
super(layout);
newClassButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
addResizer();
}
});
deleteButton = new JButton("Delete");
deleteButton.addActionListener(this);
this.addMouseListener(this);
this.add(newClassButton);
this.add(deleteButton);
}
public void addResizer() {
//JPanel panel = new JPanel();
//panel.setBackground(Color.white);
resizer = new Resizable( new ClassBox());
this.add(resizer);
this.revalidate();
this.repaint();
}
public void actionPerformed(ActionEvent e) {
if(current!=null)
{
this.remove(current);
this.revalidate();
this.repaint();
}
}
public void mouseClicked(MouseEvent e) {
System.out.println(e);
Component component = e.getComponent();
if(component instanceof Resizable)
current= (Resizable) e.getComponent();
}
public static void main(String[] args) {
JFrame jframe = new JFrame();
jframe.add(new MainDisplayPanel(null));
jframe.setSize(new Dimension(600,400));
jframe.setVisible(true);
jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
Doh!
Now, in the addResizer() method. Every time I press the add button to add a new Resizable object, what'd happen to the previously added objects? I'm certain that they become null because resizer variable no longer referring to it them??? Even if this is the case, they are still displayed on the panel...And if I pressed delete only the newly added Resizable object gets removed. So am I on the right track here?
Edit: to sum up my problem, I hooked the MouseListener to wrong object. It should be Resizable object instead of the panel. Therefore, variable current is always null.

Your problem is your MouseLisetener. You are listening to the MainDisplayPanel, and so when you click on the JPanel, the MouseEvent#getComponent method returned by, e, in your mousePressed method will return the MainDisplayPanel instance since that is what is being listened to, not the Resizable instance that is under the mouse.
Solutions include:
creating one MouseListener object and adding this same object to each Resizable as a MouseListener for the Resizable, or
using your current set up, but hold your Resizable's in an ArrayList and then iterating through the array list in the mousePressed method to see if any Resizable has been clicked by using the componentAt(...) method.
Note that I had to create my own SSCCE to solve this. Again in the future, please do us all a favor and do this for us as it really is in your and our best interest, and shows that you respect our time and our help.
Edit 1
My SSCCE:
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.swing.*;
#SuppressWarnings("serial")
public class MainDisplayPanel extends JPanel {
private static final int RESIZABLE_COUNT = 40;
private JButton deleteButton;
private Resizable current;
private Resizable resizer;
private List<Resizable> resizableList = new ArrayList<Resizable>();
public MainDisplayPanel(LayoutManager layout) {
super(layout);
deleteButton = new JButton("Delete");
deleteButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
deleteButtonActionPerformed(e);
}
});
this.addMouseListener(new MyMouseAdapter());
this.add(deleteButton);
for (int i = 0; i < RESIZABLE_COUNT; i++) {
addResizer();
}
}
private void deleteButtonActionPerformed(ActionEvent e) {
if (current != null) {
this.remove(current);
resizableList.remove(current);
current = null;
this.revalidate();
this.repaint();
}
}
public void addResizer() {
resizer = new Resizable();
this.add(resizer);
resizableList.add(resizer);
this.revalidate();
this.repaint();
}
private class MyMouseAdapter extends MouseAdapter {
#Override
public void mousePressed(MouseEvent e) {
current = null;
Component c = getComponentAt(e.getPoint());
for (Resizable resizable : resizableList) {
if (resizable == c) {
current = resizable;
resizable.setFill(true);
} else {
resizable.setFill(false);
}
}
}
}
public static void main(String[] args) {
JFrame jframe = new JFrame();
// !! jframe.add(new MainDisplayPanel(null));
jframe.add(new MainDisplayPanel(new FlowLayout()));
jframe.setSize(new Dimension(600, 400));
jframe.setVisible(true);
jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
#SuppressWarnings("serial")
class Resizable extends JPanel {
private static final int RESIZE_WIDTH = 50;
private static final int RESIZE_HEIGHT = 40;
private static final int THICKNESS = 5;
private static final Color FILL_COLOR = Color.pink;
public Resizable() {
Random rand = new Random();
// different color border so we can see that it was the clicked one that was deleted.
Color color = new Color(
rand.nextInt(255),
rand.nextInt(255),
rand.nextInt(255));
setBorder(BorderFactory.createLineBorder(color, THICKNESS));
}
#Override // so we can see it
public Dimension getPreferredSize() {
return new Dimension(RESIZE_WIDTH, RESIZE_HEIGHT);
}
public void setFill(boolean fill) {
Color fillColor = fill ? FILL_COLOR : null;
setBackground(fillColor);
repaint();
}
}

it very crazy idea, but everything is possible, but
1) in case that you Layed JComponent by using some of LayoutManager you can remove JComponents from Container, and thenafter you must/have to call revalidate() + repaint(), but this actions has side effect -> ReLayout Container and then Container's contents could be look very ***
2) in case that you layed Container with AbsoluteLayout, that should be maybe nicest but question is what with emtpy space inside Container
there is very easy way how to do it, you need to add JPopupMenu to the Container,
on RightMouseClick you have to finding JComponent under the MouseCursor
then call Container#remove(myComponent), thenafter you have to call revalidate() + repaint() for refresh GUI
or is same for me
call myComponent.setVisible(false), no re-layout, no revalidate + repaint, JComponent waiting on same place for (eventually) reusing
excelent thread about how to LayoutManagers add/remove JComponents + revalidate + repaint

I believe the problem is you need to force Swing to layout the components again after removing one. After you remove(current), call revalidate().