I am starting learning Java, and I wanted to create a simple camera feed viewer using OpenCV.
MyCV class works just fine when instantiated from its own main() method, or when the call is made from within the main() method of a caller class.
I then built a "MyClient" class, with a main() method and a simple GUI (just a JFrame and a JButton, really), because I want MyCV GUI to be shown when pressing a button in MyClient GUI.
The problem is, when the "caller" class has its own JFrame and associated GUI elements, and I click the button, the whole GUI freezes, the frame from MyCV class shows up empty, and both windows become unresponsive.
I've also tried the class with SwingUtilities.invokeLater() , to no avail.
As I said, I'm a novice at Java/Swing, and it looks to me like a paintComponent() issue, but for the life of me, I can't fix it.
Any help is greatly appreciated
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.core.Point;
import org.opencv.core.Scalar;
import org.opencv.core.Size;
import org.opencv.imgproc.Imgproc;
import org.opencv.videoio.VideoCapture;
public class MyCV {
public static void main(String args[]){
MyCV cv=new MyCV();
}
public MyCV(){
System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
//-- Video capture structure
VideoCapture feed=new VideoCapture(0);
//-- Mat structures
Mat imgFeed1=new Mat();
Mat imgFeed2=new Mat();
Mat imgFeed3=new Mat();
Mat imgFeed4=new Mat();
imgPanel feedPanel1=new imgPanel(); feedPanel1.setPreferredSize(new Dimension(400,400));
imgPanel feedPanel2=new imgPanel(); feedPanel2.setPreferredSize(new Dimension(400,400));
imgPanel feedPanel3=new imgPanel(); feedPanel3.setPreferredSize(new Dimension(400,400));
imgPanel feedPanel4=new imgPanel(); feedPanel4.setPreferredSize(new Dimension(400,400));
JPanel container=new JPanel(); container.setPreferredSize(new Dimension(800,800));
container.add(feedPanel1);
container.add(feedPanel2);
container.add(feedPanel3);
container.add(feedPanel4);
JFrame f=new JFrame("MyChild");
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
f.add(container);
f.setSize(1300, 800);
f.setVisible(true);
//-- clear resources on exit
f.addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
feed.release();
f.dispose();
}
});
//-- main loop
while(true){
if(!feed.isOpened()) break;
feed.read(imgFeed1);
if(imgFeed1.size().width==0) break;
//-- display images in panels (Colors +Feed +Norm)
feedPanel1.setimagewithMat(imgFeed1);
feedPanel2.setimagewithMat(imgFeed1);
feedPanel3.setimagewithMat(imgFeed1);
feedPanel4.setimagewithMat(imgFeed1);
// repaint frame
container.repaint();
}
}
class imgPanel extends JPanel{
private static final long serialVersionUID=1L;
private BufferedImage image;
//public imgPanel(){ super(); }
private BufferedImage getimage(){ return image; }
public void setimage(BufferedImage newimage){image=newimage; return; }
//-- called method
public void setimagewithMat(Mat newimage){
image=matToBufferedImage(newimage);
return;
}
//--
//--
public BufferedImage matToBufferedImage(Mat matrix) {
int cols = matrix.cols();
int rows = matrix.rows();
int elemSize = (int)matrix.elemSize();
byte[] data = new byte[cols * rows * elemSize];
int type;
matrix.get(0, 0, data);
switch (matrix.channels()) {
case 1:
type = BufferedImage.TYPE_BYTE_GRAY;
break;
case 3:
type = BufferedImage.TYPE_3BYTE_BGR;
// bgr to rgb
byte b;
for(int i=0; i<data.length; i=i+3) {
b = data[i];
data[i] = data[i+2];
data[i+2] = b;
}
break;
default:
return null;
}
BufferedImage image2 = new BufferedImage(cols, rows, type);
image2.getRaster().setDataElements(0, 0, cols, rows, data);
return image2;
}
#Override
protected void paintComponent(Graphics g){
super.paintComponent(g);
BufferedImage temp=getimage();
if(temp!=null){
g.drawImage(temp, 0, 0, temp.getWidth(), temp.getHeight(), this);
}
}
}
}
MyClient.java:
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
public class MyClient {
public static void main(String args[]){
//MyCV cv=new MyCV();
//MyClient cli=new MyClient();
JFrame f=new JFrame("My Client");
f.setSize(300, 300);
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
f.setVisible(true);
JButton button=new JButton("call Color Detector");
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
MyCV cv=new MyCV();
}
});
f.add(button);
}
public MyClient(){
JFrame f=new JFrame("My Client");
f.setSize(300, 300);
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
f.setVisible(true);
JButton button=new JButton("call Color Detector");
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
MyCV cv=new MyCV();
}
});
f.add(button);
}
}
while(true){
The above is an infinite loop that runs on the Event Dispatch Thread (aka EDT). Swing is single threaded - all events, painting, etc...occur on a single thread (the EDT) - if that Thread is for any reason tied up doing work none of its other responsibilities can occur (in other words, it looks like your user interface locks up). The main method runs on a separate Thread, so you do not see the same behavior (although all calls to Swing components should be placed on the EDT so I would not necessarily call this the correct way to get around the behavior). Three options:
Start one or more new Threads and place any long running tasks within that thread (note that any calls to Swing Components should be placed on the EDT using SwingUtilities)
Use a SwingWorker
If you wish to do something periodically, such as animation, you can use a java.swing.Timer
An example of 1:
//long running task inside a new Thread
new Thread(new Runnable(){
#Override
public void run(){
while(true){
}
}
});
Related
I wanted to create a JFrame and put a sequence of images for animation in there. But the images don't appear in the frame window. I just want basic troubleshooting tips to make it appear in the window. Just edit the code for an answer if you can.
My question:
Why isn't the window displaying any pictures? It shows a window with a background color of blue, but that's it. Please tell me an efficient way to store images in variables and display it in a loop.
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import javax.imageio.ImageIO;
import javax.swing.*;
import java.io.*;
public class Game extends JLabel implements ActionListener{
/**
*
*/
private static final long serialVersionUID = 1L;
public static Game blah;
BufferedImage nekopics[] = new BufferedImage[7];
BufferedImage currentimg;
public String nekosrcs[];
int xpos;
Timer timer;
public Game() throws IOException
{
JFrame jframe = new JFrame();
nekosrcs = new String[] { "walk1.png", "walk2.png",
"walk3.png", "walk4.png", "walk5.png",
"walk6.png"};
jframe.setTitle("Game");
jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jframe.setLayout(new FlowLayout());
jframe.setSize(400, 400);
jframe.setResizable(false);
jframe.setVisible(true);
jframe.getContentPane().setBackground(Color.BLUE);
for (int i=0; i < nekopics.length; i++) {
nekopics[i] = ImageIO.read(new FileInputStream("D:/Programs
/pics"+nekosrcs[i]));
}
for (int i=0; i < nekopics.length; i++) {
timer = new Timer(1000, this);
timer.setInitialDelay(0);
timer.start();
currentimg = nekopics[i];
repaint();
}
}
public void paintComponent(Graphics g)
{
super.paint(g);
g.drawImage(currentimg,100,100,this);
}
public static void main(String[] args) throws IOException {
blah = new Game();
}
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
}
}
Alright, there are a lot of problems in your code, let's step into each of them:
You have a lot of spaces between lines, that makes your code a lot larger and harder to read
You haven't indented your code correctly (see the last } on your code, it's at the same level than the others; your for loops, etc), it makes the code so much harder to read and understand as well
You're creating a JFrame but extending JLabel, I'm not sure why you're doing this, if you're doing it so you can use the paintComponent() method, it's not necessary, on my code you can see how you can do it w/o extending any Component
If you haven't read the Swing Timer docs you should click that link and read what the ActionListener parameter does. In this case, we're going to use this listener to call the repaint() method and update our currentImage (or nextImage in the code below) and change the image accordingly. You failed to do this.
You were creating more than 1 Timer too, you created 6 here! All of them new but they had no action to do when the time finished
for (int i=0; i < nekopics.length; i++) {
timer = new Timer(1000, this);
timer.setInitialDelay(0);
timer.start();
currentimg = nekopics[i];
repaint();
}
You're changing unnecessarily the visibility of the paintComponent() method to public from protected
However I want to congratulate you for not using a null layout and following the recommendations I made on the comments above.
And finally the code that changes one image for another inside a Timer is the following, you can copy-paste it and change the image's names so you can see how it works.
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.FileInputStream;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class ImageSequence {
private JFrame frame;
private JPanel pane;
private Timer timer;
private int nextImage = 0;
private String[] images = {"tokyo", "tokyo2", "starwars"};
private Image img = null;
public static void main (String args[]) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new ImageSequence().createAndShowGui();
}
});
}
public void createAndShowGui() {
frame = new JFrame("Image Sequence");
timer = new Timer(1000, listener);
pane = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
try {
img = ImageIO.read(new FileInputStream("/home/jesus/Pictures/" + images[nextImage] + ".jpg"));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
g.drawImage(img , 0, 0, 200, 200, this);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
};
timer.start();
frame.getContentPane().add(pane);
frame.pack();
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
ActionListener listener = new ActionListener() {
#Override
public void actionPerformed(ActionEvent event) {
System.out.println(nextImage);
nextImage = nextImage < images.length - 1 ? nextImage + 1 : 0;
System.out.println(nextImage);
pane.repaint();
}
};
}
I am trying to make a thread that reads the screen and displays it in a frame, this code is meant to run at 5fps, so far it reads the screen, but I am having trouble making the JFrame display the updating Image each "frame" or 200 mili-seconds. when I use repaint(); or revalidate();
public static void startScreenRecorder()
{
Thread screenThread = new Thread()
{
public synchronized void run()
{
long time;
long lastFrameTime = 0;
JFrame frame = new JFrame("Screen capture");
ImagePanel panel = new ImagePanel(captureScreen());
frame.add(panel);
frame.setSize(300, 400);
frame.setVisible(true);
while (true)
{
time = System.currentTimeMillis();
while (time - lastFrameTime < 190)
{
try {
Thread.sleep(10);
} catch (Exception e) {
}
time = System.currentTimeMillis();
}
lastFrameTime = time;
panel = new ImagePanel(captureScreen());
panel.revalidate();
panel.repaint();
frame.revalidate();
frame.repaint();
}
}
};
screenThread.start();
}
Don't use Thread.sleep() to attempt to control animation.
Animation should be done by using a Swing Timer. When you use a Timer the GUI is automatically updated on the EDT.
panel = new ImagePanel(captureScreen());
The above code doesn't do anything. It just creates a panel in memory. Nowhere to you actually add the panel to the GUI. Changing the reference of a variable does not update the GUI.
Instead you should probably add a JLabel to the frame (when you initially create the frame). Then when you have a new Image you just do:
label.setIcon( new ImageIcon( your screen capture ) );
I wouldn't be surprised if your code shows no images at all since it ignores Swing threading rules:
All Swing code needs to be called on the Swing event dispatch thread (EDT) only.
All other long-running code needs to be called in a background thread. I assume that this means captureScreen().
You should never call Thread.sleep(...) on the Swing event thread unless you want to put your entire application to sleep.
Better perhaps to use a Swing Timer.
You create new ImagePanels but do nothing with them -- you never add them to the GUI for instance, except for the first JPanel. Note that if you change the object a variable refers to, here the panel variable, this will have absolutely no effect on instances of the object used elsewhere, there the JPanel displayed in the GUI.
Rather than create new JPanels, why not instead create ImageIcons with your images and swap a visualized JLabel's Icon with setIcon(...)?
Since you have a lot of background stuff going on, consider using a SwingWorker<Void, Icon> to do your work, and have it publish ImageIcons that are then displayed in the GUI's JLabel. If you did this, then you probably wouldn't use a Swing Timer since the timing would be done in the SwingWorker's background thread.
For example:
import java.awt.AWTException;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.image.BufferedImage;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;
#SuppressWarnings("serial")
public class SwingWorkerEg extends JPanel {
private static final int PREF_W = 600;
private static final int PREF_H = 400;
private JLabel displayedLabel = new JLabel();
public SwingWorkerEg() {
setLayout(new BorderLayout());
add(displayedLabel);
try {
MySwingWorker mySwingWorker = new MySwingWorker();
mySwingWorker.execute();
} catch (AWTException e) {
e.printStackTrace();
}
}
public void setLabelIcon(Icon icon) {
displayedLabel.setIcon(icon);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
private class MySwingWorker extends SwingWorker<Void, Icon> {
private final Rectangle SCREEN_RECT = new Rectangle(0, 0, PREF_W,
PREF_H);
private Robot robot = null;
public MySwingWorker() throws AWTException {
robot = new Robot();
}
#Override
protected Void doInBackground() throws Exception {
Timer utilTimer = new Timer();
TimerTask task = new TimerTask() {
#Override
public void run() {
BufferedImage capturedImage = captureScreen();
publish(new ImageIcon(capturedImage));
}
};
long delay = 200;
utilTimer.scheduleAtFixedRate(task, delay, delay);
return null;
}
#Override
protected void process(List<Icon> chunks) {
for (Icon icon : chunks) {
setLabelIcon(icon);
}
}
private BufferedImage captureScreen() {
BufferedImage img = robot.createScreenCapture(SCREEN_RECT);
return img;
}
}
private static void createAndShowGui() {
SwingWorkerEg mainPanel = new SwingWorkerEg();
JFrame frame = new JFrame("SwingWorker Eg");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
Which would display...
This is a really general question, but how should I add an animated background for a JPanel. I want the background to be behind all the panel's components and graphics. Right now, I have two separate classes (one for the main panel and the other for the background). The background class uses repaint() to animate a grid moving across the screen. I've tried to make the main panel background transparent, but that hasn't gotten me anywhere.
Even more info:
My main panel is part of a CardLayout and it has many different classes in it. So when I'm adding my main panel to my main frame, I'm doing frame.getContentPane().add(cards, BorderLayout.CENTER)
cards is a JPanel which acts as a container for the mainpanel and all the panels inside main panel.
Can anybody help me out in getting a panel animated background?
You can use Toolkit.getImage() to load animated image and then draw the image in container's paintComponent. Make sure the ImageObserver is set (not null) in order to update animation frames properly. For details how image is loaded, observed and updated see How Images are Loaded appendix in Java AWT Reference.
Here is a simple example:
import java.awt.*;
import javax.swing.*;
import java.net.URL;
class AnimatedPanelDemo {
static class ImagePanel extends JPanel {
private Image image;
ImagePanel(Image image) {
this.image = image;
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(image,0,0,getWidth(),getHeight(),this);
}
}
private static void createAndShowUI() {
try {
JFrame frame = new JFrame("Image");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
Image image = Toolkit.getDefaultToolkit().getImage(new URL(
"http://duke.kenai.com/iconSized/duke.running.gif"));
ImagePanel imagePanel = new ImagePanel(image);
imagePanel.add(new JLabel("Some label"));
frame.add(imagePanel);
frame.setSize(100, 100);
frame.setVisible(true);
}
catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowUI();
}
});
}
}
Well, this is my first answer on stackoverflow.
Will try to help with my learning curve with this complex AWT and Swift API.
Below there's the contructor that extends JFrame
package xpto;
import java.awt.Dimension;
import java.awt.GraphicsConfiguration;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.Toolkit;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.awt.event.WindowStateListener;
import java.awt.image.ImageObserver;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import sun.java2d.SunGraphicsEnvironment;
import java.awt.Graphics;
import java.awt.Graphics2D;
public class FrameLuckyRaffle extends JFrame {
/**
*
*/
private JLabel backgroundLabel;
private ImageIcon imageIcon;
private Image bgImage;
/**
* Constructor of this frame.
*/
public FrameLuckyRaffle(String background, final String dbname) {
try {
setTitle("Lucky Raffle of "+ dbname);
GraphicsConfiguration config = this.getGraphicsConfiguration();
Rectangle usableBounds = SunGraphicsEnvironment.
getUsableBounds(config.getDevice());
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
setBounds(100, 100, (int)(usableBounds.getWidth()*0.8),
(int)(usableBounds.getHeight()*0.8));
setMinimumSize(new Dimension(1024, 700));
setResizable(true);
setDefaultLookAndFeelDecorated(true);
backgroundLabel = new JLabel() {
public void paintComponent(Graphics g) {
// alternative --> g.drawImage(bgImage, 0, 0, null);
// I prefer to control the new ImageObserver parameter as bellow
g.drawImage(bgImage, 0, 0, new ImageObserver() {
#Override
public boolean imageUpdate(Image img, int infoflags,
int x, int y, int width, int height) {
img.getScaledInstance(getWidth(),getHeight(),
Image.SCALE_FAST);
return true;
}
});
// this is used to have easier control on
// image manipulation on my application
Graphics2D g2d = (Graphics2D)g;
super.paintComponent(g2d);
revalidate();
repaint();
}
};
backgroundLabel.setBounds(0, 0, 0, 0);
// this is necessary if you want more child
// components to be visible on the JFrame afterwards
backgroundLabel.setOpaque(false);
setContentPane(backgroundLabel);
addWindowListener(new WindowListener() {
#Override
public void windowOpened(WindowEvent e) {
// Set Frame Background
imageIcon = new ImageIcon(Toolkit.getDefaultToolkit().
createImage(FrameBusinessPure.class.getResource(background)));
bgImage = imageIcon.getImage().
getScaledInstance(getWidth(),getHeight(), Image.SCALE_FAST);
}
// Even after closing the window, JVM didn't Garbage Collected the instanced
// objects, for some reason. Forcing the objects to null helped on that.
#Override
public void windowClosed(WindowEvent e) {
backgroundLabel = null;
imageIcon = null;
bgImage = null;
System.gc();
}
});
addWindowStateListener(new WindowStateListener() {
#Override
public void windowStateChanged(WindowEvent e) {
// if you flush the object on runtime you will surpass the
// memory leak on using GIFs and most complex graphics
bgImage.flush();
bgImage = imageIcon.getImage().
getScaledInstance(getWidth(),getHeight(), Image.SCALE_FAST);
}
});
addMouseMotionListener(new MouseMotionListener() {
#Override
public void mouseDragged(MouseEvent e) {
// if you flush the object on runtime you will surpass the
// memory leak on using GIFs and most complex graphics
bgImage.flush();
bgImage = imageIcon.getImage().
getScaledInstance(getWidth(),getHeight(), Image.SCALE_FAST);
});
}catch (Exception e) {
e.printStackTrace();
}
}
}
Feel free to learn more on below link
https://www.oracle.com/java/technologies/painting.html
I am very new to Java AWT. My question header must seem ridiculous to you, sorry about that. In my application I have three buttons which display different threads when clicked on. Now I want to add maybe a button or checkboxes or choicelist, etc when clicked on a particular button. For eg, if I click on yes button, it should display a choice list, something like that. How do I achieve something like that? Here is my code so far:
import java.awt.Button;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
public class AppWindow extends Frame implements ActionListener{
String keymsg = "Test message";
String mousemsg = "Nothing";
int mouseX=30, mouseY=30;
String msg;
public AppWindow(){
//addKeyListener(new MyKeyAdapter(this));
//addMouseListener(new MyMouseAdapter(this));
addWindowListener(new MyWindowAdapter());
}
public void paint(Graphics g){
g.drawString(msg, 150, 100);
}
//Here the window is created:
public static void main(String args[]){
AppWindow appwin = new AppWindow();
appwin.setSize(new Dimension(300,200));
appwin.setTitle("My first AWT Application");
appwin.setLayout(new FlowLayout(FlowLayout.LEFT));
appwin.setVisible(true);
Button yes,no,maybe;
yes = new Button("yes");
no = new Button("no");
maybe = new Button("maybe");
appwin.add(yes);
appwin.add(no);
appwin.add(maybe);
yes.addActionListener(appwin);
no.addActionListener(appwin);
maybe.addActionListener(appwin);
}
#Override
public void actionPerformed(ActionEvent ae) {
// TODO Auto-generated method stub
String str = ae.getActionCommand();
if(str.equals("yes")){
msg = "You pressed Yes";
}
if(str.equals("no")){
msg = "You pressed No";
}
if(str.equals("maybe")){
msg = "You pressed Maybe";
}
repaint();
}
}
class MyWindowAdapter extends WindowAdapter {
public void windowClosing(WindowEvent we){
System.exit(0);
}
}
Points describing what you should be doing :
As already mentioned by others, better to use Swing over AWT, since Swing is more advanced.
As much as possible, always try to Paint on top of a JPanel or a
JComponent, instead of Painting right on top of your JFrame, by
overriding the paintComponent(Graphics g) method of the said
JComponent/JPanel
Never call setVisible(true) on the JFrame until and unless it's
size has been established. So in general terms, this has to be the
last call, once you are done adding components to the JFrame and
the size of the JFrame has been realized by the LayoutManager.
Inside your actionPerformed(...), instead of writing all if
statement blocks, you should adhere to the if-else if statement
blocks. The benefit of this, over the former is that, at any given
time, only one event will be fired, hence once the said condition is
satisfied, you don't want your code to keep checking other
conditions, which in general is really not a good programming
practice, IMHO.
MOST IMPORTANT THING : Never make calls like pack()/setVisible(...) from within the main method, such calls belong
to the Event Dispatch Thread, and must be done on the same. Please
read Concurrency in Swing for more detail.
Have a look at the example program, for better understanding.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class ComponentExample
{
private CustomPanel drawingBoard;
private JPanel contentPane;
private JButton yesButton;
private JButton noButton;
private JButton maybeButton;
private JComboBox cbox;
private ActionListener buttonAction = new ActionListener()
{
#Override
public void actionPerformed(ActionEvent ae)
{
JButton button = (JButton) ae.getSource();
if (cbox.isShowing())
contentPane.remove(cbox);
if (button == yesButton)
{
drawingBoard.setText("You Pressed YES.");
contentPane.add(cbox, BorderLayout.PAGE_END);
}
else if (button == noButton)
drawingBoard.setText("You Pressed NO.");
else if (button == maybeButton)
drawingBoard.setText("You Pressed MAYBE.");
/*
* revalidate()/repaint() is needed
* when the JComponent is added or
* removed from the already
* visible Container.
*/
contentPane.revalidate();
contentPane.repaint();
}
};
public ComponentExample()
{
cbox = new JComboBox(
new String[]{"I GOT IT"
, "I STILL HAD DOUBT"});
}
private void displayGUI()
{
JFrame frame = new JFrame("Component Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
contentPane = new JPanel();
contentPane.setOpaque(true);
contentPane.setBackground(Color.DARK_GRAY);
contentPane.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
contentPane.setLayout(new BorderLayout(5, 5));
JPanel buttonPanel = new JPanel();
buttonPanel.setOpaque(true);
buttonPanel.setBackground(Color.WHITE);
yesButton = new JButton("YES");
yesButton.addActionListener(buttonAction);
noButton = new JButton("NO");
noButton.addActionListener(buttonAction);
maybeButton = new JButton("MAY BE");
maybeButton.addActionListener(buttonAction);
buttonPanel.add(yesButton);
buttonPanel.add(noButton);
buttonPanel.add(maybeButton);
contentPane.add(buttonPanel, BorderLayout.PAGE_START);
drawingBoard = new CustomPanel();
contentPane.add(drawingBoard, BorderLayout.CENTER);
frame.setContentPane(contentPane);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String... args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
new ComponentExample().displayGUI();
}
});
}
}
class CustomPanel extends JPanel
{
private String msg;
public CustomPanel()
{
msg = "";
setOpaque(true);
setBackground(Color.WHITE);
}
public void setText(String msg)
{
this.msg = msg;
repaint();
}
#Override
public Dimension getPreferredSize()
{
return (new Dimension(300, 300));
}
#Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
g.drawString(msg, getWidth() / 3, getHeight() / 3);
}
}
I don't know if I have understood the question well but... couldn't you create those elements and call their setVisible(boolean) methods to make them not visible at first, and them make them visible when user pushes buttons?
I have been searching for an answer to this for two days now, but that didn't seem to solve much. Mostly because i don't really understand what is causing my error in the first place, nor would i know how to go about fixing the problem.
I've been trying to make an "animation" of sorts, where one of the layers in it spawn circles on the right side of the screen and send them to the left over time. Problem is every time it is meant to spawn a circle, it doesn't appear and i get an error.
Exception in thread "Thread-4" java.lang.NullPointerException
at Ball.draw(Ball.java:39)
at Ball.run(Ball.java:23)
Here is the class that is causing the errors:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.util.Random;
import javax.swing.JPanel;
public class Ball extends Thread{
JPanel drawingPanel;
private int x=400,y=200;
private int dx=-2,dy=0;
private static final int XSIZE=10,YSIZE=10;
Random rdm = new Random();
int y_rdm = rdm.nextInt(440)+30;
public Ball(JPanel jp){
drawingPanel=jp;
dx-=1;
}
public void run(){
draw();
for (int i=0;i<1000;i++){
try{
Thread.sleep(10);
}
catch(InterruptedException e){}
move();
}
}
private void move(){
erase();
changePos();
draw();
}
private void draw(){
Graphics g = drawingPanel.getGraphics();
g.setColor(Color.WHITE);
g.fillOval(x,y_rdm,XSIZE,YSIZE);
g.dispose();
}
private void erase(){
Graphics g=drawingPanel.getGraphics();
g.setColor(drawingPanel.getBackground());
g.fillOval(x,y_rdm,XSIZE,YSIZE);
g.dispose();
}
private void changePos(){
x+=dx;y_rdm+=dy;
}
}
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JPanel;
import javax.swing.Timer;
public class BallPanel extends JPanel implements ActionListener{
JPanel drawingPanel = new JPanel();
public BallPanel(){
int delay = 300;
ActionListener taskPerformer = new ActionListener() {
public void actionPerformed(ActionEvent evt) {
Ball b= new Ball(drawingPanel);
b.start();
}
};
new Timer(delay, taskPerformer).start();
}
#Override
public void actionPerformed(ActionEvent e) {
}
}
import java.awt.BorderLayout;
import java.awt.Color;
import java.io.InputStream;
import java.net.URL;
import javax.swing.JFrame;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
import javazoom.jl.player.Player;
public class Window extends JFrame{
private JLayeredPane layerpane;
private JPanel up, down;
public Window(){
layerpane = new JLayeredPane();
down = new JPanel();
down.setBounds(0, 0, 450, 450);
down.setBackground(new Color(0, 51, 102));
layerpane.add(down, new Integer(1));
BallPanel bp = new BallPanel();
layerpane.add(bp, new Integer(2));
bp.setBounds(0, 0, 450, 450);
bp.setOpaque(!bp.isOpaque());
Animation2 ani2 = new Ani2();
ani2.setBounds(0, 0, 400, 450);
layerpane.add(ani2, new Integer(3));
ani2.setOpaque(!ani2.isOpaque());
getContentPane().add(layerpane, BorderLayout.CENTER);
}
public static void main(String args[]){
JFrame f = new Window();
f.setVisible(true);
f.setSize(450,450);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
try{
URL url = new URL("file:///C://song.mp3");
InputStream in = url.openStream();
Player pl = new Player(in);
pl.play();
}
catch(Exception e){
e.printStackTrace();
}
}
}
Please tell me if i need to include my other classes, they just seem slightly irrelevant.
The getGraphics method of JComponent returns the Graphics object associated with the Component. But if there is no Graphics object associated it will return null, which is the case in your code.
A Component is associated with a Graphics object only when it is added to a container that is associated with one, or if it is a Top-Level Container (JFrame, JDialog, and JApplet).
Your problem here is that your JPanel is not contained inside any top-level container, so its associated Graphics object is null.
To fix the problem, either make sure you have added the JPanel to a top-level container before you call getGraphics() on it, or instead extend JPanel and override its paintComponent(Graphics g) method to do the drawing (second option is preferred since the paintComponent method is called automatically whenever the parent container needs to be redrawn (e.g. if it was resized, or blocked and unblocked by some other window, ...)).
(By the way, in your BallPanel class which extends JPanel, you define a new JPanel and pass it to Ball's constructor. You should be passing this to the the constructor, since the drawingPanel is never added to any container, but the BallPanel instance itself is. It really doesn't make sense to define a JPanel field inside a class which is itself a JPanel and have the field do the job that the class itself is supposed to do.)