Develop Reference

JPanel not displaying after button pressed in another JPanel

Hi I'm building a game which includes 3 JPanels on a JFrame, a Startscreen, a DrawingPanel and a GameOver screen. If I just create the DrawingPanel and tell the GameController class to begin updating it works fine, but if I create a StartScreen with a button to start the game, then when I press the start game button the game window does not display, although the game code runs.
EDIT:
I have created a new program which mimics the creation of the JPanels, but excludes all of the game code to make it a bit simpler to follow. Below I have included all the relevant classes:
This class creates a JFrame and two JPanels. It also runs the code that updates the game state and tells the DrawingPanel to repaint.
public class TestController{
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
private final int FRAME_WIDTH = (int)screenSize.getWidth();
private final int FRAME_HEIGHT = (int)screenSize.getHeight();
public boolean gameStarted = false;
private JFrame gameWindow;
private TestDrawingPanel myDrawingPanel;
private TestStartGame startGame;
int counter;
Set<Rectangle> rects;
//creates a JFrame and all the JPanels
public TestController(String title)
{
gameWindow = new JFrame(title);
gameWindow.setSize(FRAME_WIDTH, FRAME_HEIGHT);
gameWindow.setVisible(true);
gameWindow.setResizable(false);
gameWindow.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
startGame = new TestStartGame(getAvailableWidth(), getAvailableHeight());
startGame.addAL(new StartButton());
myDrawingPanel = new TestDrawingPanel(getAvailableWidth(), getAvailableHeight());
gameWindow.add(startGame);
gameWindow.add(myDrawingPanel);
myDrawingPanel.setVisible(false);
myDrawingPanel.setEnabled(false);
rects = new HashSet();
}
private int getAvailableWidth()
{
return gameWindow.getWidth() - gameWindow.getInsets().left - gameWindow.getInsets().right;
}
private int getAvailableHeight()
{
return gameWindow.getHeight() - gameWindow.getInsets().top - gameWindow.getInsets().bottom;
}
//starts the game running
public void startTheGame()
{
myDrawingPanel.setEnabled(true);
startGame.setVisible(false);
startGame.setEnabled(false);
myDrawingPanel.setVisible(true);
gameStarted = true;
update();
}
public boolean getGameStarted()
{
return gameStarted;
}
//loop that runs the game code
public void update()
{
counter = 0;
while(gameStarted)
{
updatePictureState();
myDrawingPanel.draw(rects);
myDrawingPanel.repaint();
}
}
//updates the game state
public void updatePictureState()
{
rects.clear();
for (int i = counter + 10; i < counter + 100; i = i + 10)
{
rects.add(new Rectangle(i,i,10,10));
}
}
//an action listener to be added to the start screen
private class StartButton implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
Object buttonPressed = e.getSource();
if(buttonPressed.equals(TestStartGame.start))
{
startTheGame();
}
}
}
}
This class is an extended JPanel with a single button to start the game:
public class TestStartGame extends JPanel{
private final JPanel buttons;
public static JButton start;
//creates a JPanel with a single button to start the game
public TestStartGame(int width, int height)
{
setSize(width, height);
setLayout(new GridLayout(2,1));
setBackground(Color.GREEN);
buttons = new JPanel();
buttons.setSize(width, height / 2);
buttons.setBackground(Color.red);
start = new JButton("Start");
buttons.add(start);
add(buttons, BorderLayout.SOUTH);
}
//adds an action listener to the button
public void addAL(ActionListener al)
{
start.addActionListener(al);
}
}
This class is an extended JPanel and acts as the main screen for the game, being updated to with each cycle of the game to display it's current state:
public class TestDrawingPanel extends JPanel{
Set<Rectangle> drawSet;
//creates the drawing panel and sets the size and background
public TestDrawingPanel(int width, int height)
{
setSize(width, height);
this.setBackground(Color.CYAN);
drawSet = new HashSet();
}
public void draw(Set<Rectangle> platforms)
{
drawSet.clear();
drawSet = platforms;
}
//draws the game window
#Override
public void paintComponent(Graphics g)
{
super.paintComponent(g);
System.out.println("works here");
g.setColor(Color.red);
for (Rectangle r : drawSet)
{
g.fillRect((int)r.getX(), (int)r.getY(), (int)r.getWidth(), (int)r.getHeight());
}
}
}
If I just add the TestDrawingPanel, it displays fine, but if I start with a TestStartScreen then when I click the start game button the TestStartScreen does not disappear and the TestDrawingPanel never displays. Interestingly, if I have both screens but do not call the update method is TestController then the start game button works correctly and the TestDrawingPanel displays, although obviously nothing happens as the update method is where the game state is changed.
I have discovered the problem is that if the TestDrawingPanel is not the only JPanel created then the call to repaint it fails.

Here:
Thread.sleep(20);
You are most likely sleeping on the Event Dispatcher Thread. That will freeze your whole application. You have to step back and look into invokeLater to ensure "correct" threading within your UI.

Problem solved courtesy of #Andrew-Thompson:
"while(gameStarted) .. No, no a thousand times no. An infinite loop will likely freeze the GUI. Use a Swing based Timer to call those code statements in the loop, in the actionPerformed method of an ActionListener"

Made a "virus", need tips

First of all, it's not really a virus that is used to spy, or steal bank accounts. I don't even know if it's a virus at all. I only made it to troll friends/people I know, and practice my programming skills. I will show you the code, then I will try to explain it a bit;
package pracatice;
import java.awt.event.*;
import javax.swing.*;
public class practice extends JFrame
{
public static boolean bool = true;
public static int x = 0;
public static int y = 0;
public static int num = 0;
public static TimerClass tc = new TimerClass();
public static Timer timer = new Timer(30, tc);
public JPanel panel = new JPanel();
public JButton btn = new JButton("press");
public practice()
{
setSize(100,100);
setTitle("Test");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setPanel();
setVisible(true);
}
public void setPanel()
{
btn.addActionListener(new listener());
panel.add(btn);
add(panel);
}
public class listener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
num = 0;
timer.start();
}
}
public static class TimerClass implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
do
{
num++;
JOptionPane optionPane = new JOptionPane("PC afected by virus");
JDialog dialog = optionPane.createDialog(null, "Virus");
dialog.setModal(false);
dialog.setLocation(x, y);
dialog.show();
updateCordinates();
}while(bool == true);
}
}
public static void updateCordinates()
{
if(x != 1100)
x += 100;
else if(x == 1100)
{
x = 0;
y += 50;
}
if(y == 650)
y =0;
}
public static void main(String[] args)
{
new practice();
}
}
So, at first it obviously builds a window, 100 X 100 px big. It adds a button that says "press". When you press, it starts a new loop, every 30 milliseconds.
every iteration of the loop, it puts in a new JOPtionPane.showMessageBox(null,...) in a slightly different location.
At first, when I just made it, I didn't know it would be unstoppable. I ran it, and had to restart my laptop. When I pressed ok, it would put in another box, in the exact same spot. When I tried to open task manager, it would automatically minimize it, and go back into the "virus" window. So, the laptop was unusable. I had to restart it, closing some of my dads tabs...
Here are a few things I would like to find out;
1) If I left this run over night, is it possible, that the laptop ran out or RAM, and if it did, what would happen?
2) Can I make it that, when I press a button on the keyboard, the whole thing just closes?
Like I said before, I was only trying to prank my friends, and the program happened to not be closable... any advice?

Yes, the computer will eventually run out of RAM. When that happens, nothing disastrous should happen other than your program crashing.
Not very easily, because JOptionPane windows don't let keyboard events get to the rest of the program. You'd need to use your own type of window instead of JOptionPane. You could then use a KeyListener that does System.exit(0).

Java Graphics Update/Repaint Graphic

I'm trying to work with the Java paint
utility and it's been a bit of a hassle.
I'm trying to do something which I assume is quite basic.
I'm drawing a square Graphic to a JPanel and then trying
to move it using repaint
import javax.swing.*;
import java.awt.*;
import java.awt.image.*;
public class testGui {
static gui gc_gui;
static int gv_x;
static int gv_y;
public static void main(String[] args) {
gc_gui = new gui();
gv_x = 50;
gv_y = 50;
gc_gui.cv_frame.setVisible(true);
}
public static class gui {
JFrame cv_frame;
content cv_content;
public gui() {
cv_frame = new JFrame();
cv_frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
cv_frame.setTitle("Test GUI");
cv_frame.setSize(600, 400);
cv_frame.setLayout(new FlowLayout());
cv_content = new content();
cv_content.setBackground(Color.Black);
cv_content.setPreferredSize(new Dimension(500, 300));
cv_frame.add(cv_content);
gv_x = 0;
gv_y = 0;
cv_content.update();
}
}
public static class content extends JPanel {
public void paint(Graphics graphic) {
super.paint(graphic);
draw(graphic);
}
public void update() {
super.repaint();
}
public void draw(Graphics graphic) {
Graphics2D graphic2D = (Graphics2D) graphic;
graphic2D.setPaint(Color.Red);
graphic2D.fillRect(gv_x, gv_y, 100, 100);
}
}
}
I don't know why the call to the update function isn't doing
anything though.
It draws the square at 50x and 50y, the sets it to 0x and 0y
immediately and then when I call repaint I expected it to
be moved to it's new coordinates although it's still at
50x and 50y.
Why is this?

Your solution is to use KeyBindings.
https://docs.oracle.com/javase/tutorial/uiswing/misc/keybinding.html
and also.
You need to create a Swing Timer, Thread, or Loop , that manages the frames to be painted. and such
Here is a link for Swing Timers as they are pretty easy to implement:
https://docs.oracle.com/javase/tutorial/uiswing/misc/timer.html
A lot of programs I see also have this ( AKA. working with threads.):
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});

JFrame and GlassPane - Trouble with repaint()

This question may be a simple matter of me lacking a fundamental understanding of Java Swing or Graphics, and if so, I apologize.
I'm trying to develop a GUI application using Java Swing that can be controlled by an external device that sends pitch, yaw, and roll values via bluetooth to the Application. My idea is to create a cursor (perhaps an empty circle) that moves around when the external device moves around. I have no problems with receiving the data from the device, just the part where I need to actually paint something over all of my components.
I figured that a GlassPane was the easiest way to show a cursor over the entire application, and have it move around when the external device is moved around. I use a Thread to capture the data, and I'm trying to call repaint() afterwards, but it doesn't seem to be triggering.
Here is the relevant code:
JFrame:
public class Frame extends JFrame {
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
//Thread myoHandlerThread = new Thread(myoHandler);
//myoHandlerThread.start();
Frame frame = new Frame();
GlassPane glassPane = new GlassPane();
glassPane.setVisible(true);
frame.setGlassPane(glassPane);
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public Frame() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(50, 50, 1000, 650);
/* Code to add and place components */
}
}
And my GlassPane:
public class GlassPane extends JComponent {
private static double pitch;
private static double yaw;
private static double roll;
Point point;
public void setPoint(Point p) {
this.point = p;
}
public void paintComponent(Graphics g) {
if (point != null) {
System.out.println("Test print statement");
g.setColor(Color.red);
g.fillOval(point.x - 10, point.y - 10, 20, 20);
}
}
public GlassPane() {
Thread handler = new Thread(deviceHandler);
handler.start();
}
private Runnable deviceHandler = new Runnable() {
#Override
public void run() {
Hub hub = new Hub("com.garbage");
System.out.println("Attempting to find device...");
Device externalDevice = hub.waitForDevice(10000);
if (externalDevice == null) {
throw new RuntimeException("Unable to find device!");
}
System.out.println("Connected");
DataCollector dataCollector = new DataCollector();
hub.addListener(dataCollector);
while (true) {
hub.run(1000/20); //gathers data and stores in dataCollector
roll = dataCollector.getRoll();
pitch = dataCollector.getPitch();
yaw = dataCollector.getYaw();
Point p = new Point();
p.setLocation(Math.abs(pitch) * 10, Math.abs(yaw) * 10);
setPoint(p);
repaint();
}
}
};
}
What I would like to happen is for a red circle to be drawn somewhere on the GUI depending on the orientation of the external device. At this point, my "test print statement" doesn't fire even once.
My guess is that I'm lacking some sort of basic understanding of Java's GlassPane or even how paint, paintComponent, and repaint even works. Could anyone point out what I'm doing wrong?

The likely cause of your frustration is trying to set the glass pane visible (Swing components are visible by default), before setting it as the frames GlassPane.
The JFrame is likely resetting the glass pane to be invisible, meaning that it won't be painted (no point painting something that's not visible)
Try setting the glass pane visible AFTER you apply it to the frame

How to change position of a JLabel?

I'm trying to use a timer to change the position of a JLabel, from one spot on my JPanel to another. I'm not sure if I could use say .getLocation(), then change only the horizontal x value, and finally use .setLocation() to effectively modify the JLabel. I've also used .getBounds and .setBounds, but am still unsure how I can obtain the old horizontal x value to change and reapply to the new x value.
The code I tried looks something like this, but neither is a valid way to change the position of the JLabel.
// mPos is an arraylist of JLabels to be moved.
for(int m = 0; m < mPos.size(); m++){
mPos.get(m).setLocation(getLocation()-100);
}
or
for(int m = 0; m < mPos.size(); m++){
mPos.get(m).setBounds(mPos.get(m).getBounds()-100);
}
If I could just get the position of the horizontal x value I can change the position of the label.

Try with Swing Timer if you are looking for some animation.
Please have a look at How to Use Swing Timers
Here is the sample code:
int delay = 1000; //milliseconds
ActionListener taskPerformer = new ActionListener() {
public void actionPerformed(ActionEvent evt) {
//...Perform a task...
}
};
new Timer(delay, taskPerformer).start();
Find a Sample code here
Sample code: (Move Hello World message 10px horizontally left to right at interval of 200 ms)
private int x = 10;
...
final JPanel panel = new JPanel() {
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawString("Hello World", x, 10);
}
};
int delay = 200; // milliseconds
ActionListener taskPerformer = new ActionListener() {
public void actionPerformed(ActionEvent evt) {
x += 10;
if (x > 100) {
x = 10;
}
panel.repaint();
}
};
new Timer(delay, taskPerformer).start();

I made a similar example just so you can get the basic jest of it, try copy pasting this in a new class called "LabelPlay" and it should work fine.
import java.awt.EventQueue;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class LabelPlay {
private JFrame frame;
private JLabel label;
private Random rand;
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
LabelPlay window = new LabelPlay();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
public LabelPlay() {
initialize();
}
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 659, 518);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
label = new JLabel("YEEEHAH!");
label.setBounds(101, 62, 54, 21);
frame.getContentPane().add(label);
JButton btnAction = new JButton("Action!");
rand = new Random();
btnAction.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
int a = rand.nextInt(90)+10;
int b = rand.nextInt(90)+10;
int c = rand.nextInt(640)+10;
int d = rand.nextInt(500)+10;
label.setBounds(a, b, c, d);
}
});
btnAction.setBounds(524, 427, 89, 23);
frame.getContentPane().add(btnAction);
}
}
If you want this to happen in a loop at certain times, you can just put it in a loop and use Thread.sleep(amount of miliseconds) in the loop before you run the code.

Why don't you create a JLabel at position a, set it to visible, and another one at position b, setting it to not visible? After the timer is up, hide the first and show the second.

Are you planning on creating some moving imageIcon for some type of game? Or some label that moves pretty much everywhere ?
I would use an Absolute Layout and set Location manually everytime.
myPanel.setLayout(null);
// an initial point
int x = 100;
int y =100;
while (
//some moving pattern
x++; // 1 pixel per loop
y+=2; // 2 pixels per loop
myLabel.setLocation(x,y);
}