I'm making my first Applet. I have a JPanel which creates a Swing GUI and performs CPU intensive tasks (repainting a Component 60Hz). My Applet displays this JPanel on event dispatching thread. here is an abstraction of the problem. Normally I would launch the applet from an html document instead of having a main method. This program puts about a 40% load on my CPU.
import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.event.*;
public class TestApplet extends JApplet {
TestPanel tp;
public void init() {
try {
SwingUtilities.invokeAndWait(new Runnable() {
public void run() {
createGUI();
}
});
} catch (Exception e) {
System.err.println("createGUI didn't complete successfully");
}
}
private void createGUI() {
//Create and set up the content pane.
tp = new TestPanel();
tp.setOpaque(true);
setContentPane(tp);
}
public static void main(String[] args) {
JFrame f = new JFrame("Fish Tank");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JApplet ap = new TestApplet();
ap.init();
f.add("Center", ap);
f.pack();
f.setVisible(true);
}
}
class TestPanel extends JPanel{
public TestTank tt = new TestTank();
public TestPanel() {add(tt);}
public void stop() {tt.stop();}
public void start() {tt.start();}
}
class TestTank extends Component implements ActionListener{
private javax.swing.Timer timer;
TestTank(){
timer = new javax.swing.Timer(17, this);
timer.setCoalesce(true);
timer.start();
}
public Dimension getPreferredSize(){
return new Dimension(900, 700);
}
public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
Dimension size = getSize();
g2.setPaint(new GradientPaint(0,0,Color.RED,900, 0,Color.WHITE));
g2.fill(new Rectangle2D.Float(0,0,size.width,size.height));
}
public void actionPerformed(ActionEvent e) {
repaint();
}
public void stop(){timer.stop();}
public void start(){timer.start();}
}
My question: How do I suspend and resume execution of the JPanel (FishTankPanel) when the user switches tabs or minimizes the browser? I want the Applet to stop using the CPU when the user can't see what it is doing. I need to capture browser events in order to execute tp.stop() in the applet. I have tried to execute them with window event listeners in the JPanel, and by overriding the start() and stop() methods in the Applet. I have been unsuccessful. Any suggestions or solutions would be appreciated.
I would do as Dave said and use the JApplet override start and stop methods to call your GUI methods. For instance, see changes in code:
public class TestApplet extends JApplet {
TestPanel tp;
public void init() {
// ... no change
}
private void createGUI() {
// ... no change
}
#Override
public void stop() {
if (tp != null) {
tp.stop();
}
}
#Override
public void start() {
if (tp != null) {
tp.start();
}
}
}
class TestTank extends Component implements ActionListener {
private javax.swing.Timer timer;
// ... no change
public void stop() {
timer.stop();
System.out.println("stop");
}
public void start() {
timer.start();
System.out.println("start");
}
}
It seems you might need to leverage some JS for this. E.G. use the JS shown in this answer to explicitly call the applet start() & stop() methods on focus & blur detection respectively.
The solution for my problem was to use javascript to implement the Page Visibility API. I then called the appropriate Java methods from within the javascript script.
Related
I am trying to show a label from another class. However when I add it to the frame it will not show. I have tried drawing it from the counter class itself by passing in the Frame which I would assume is not good practice (ignoring the fact it didn't work). As well as what is in the code below. Can anybody help me and explain why my solution will not show the created label? As you can most likely tell i'm very new to using JPanel.
CookieChaser Class
public class CookieChaser extends JPanel {
public static void main(String[] args) throws InterruptedException {
JFrame frame = new JFrame("Cookie Chaser");
CookieChaser game = new CookieChaser();
frame.add(game);
frame.setSize(1000, 1000);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
counter Score = new counter(frame);
cookie Cookie = new cookie();
JLabel item = counter.getLabel();
frame.add(item);
frame.setVisible(true);
while (true) {
game.repaint();
Thread.sleep(10);
}
}
#Override
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
}
}
Counter Class
public class counter {
int count;
static JLabel text;
public counter(JFrame frame){
count = 0;
text = new JLabel(String.valueOf(count));
text.setLocation(0,0);
text.setSize(50,50);
}
public static JLabel getLabel(){
return text;
}
I modified your code to create the following Swing GUI.
Whenever I create a Swing game or application, I use the model / view / controller pattern. This means I create a GUI model. The GUI model contains all of the fields that my GUI needs. Next, I create a GUI view which reads the values from the GUI model. Finally, I create one or more GUI controllers, which update the GUI model and refresh / repaint the GUI view.
I made the following changes to your code:
I created a GUI model. I created the Counter class. All the Counter class does is hold a counter value.
I created a GUI view, which uses the GUI model. I created the JFrame, JPanel, and JLabel all in the view class. You may use more than one class to create the view. Since this view was simple, I created everything in one class.
All Swing applications must start with a call to the SwingUtilities invokeLater method. The invokeLater method puts the creation and updating of the Swing components on the Event Dispatch thread. Oracle and I insist that all Swing applications start this way.
I created a separate Animation runnable so that you can see the JLabel updates. I increment the counter once a second.
The repaint method in the Animation class calls the SwingUtilities invokeLater method to ensure that the JLabel update is done on the Event Dispatch thread. The animation loop runs in a separate thread to keep the GUI responsive.
Here's the revised code.
package com.ggl.testing;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class CookieChaser implements Runnable {
public static void main(String[] args) {
SwingUtilities.invokeLater(new CookieChaser());
}
private JLabel counterLabel;
#Override
public void run() {
Counter counter = new Counter();
JFrame frame = new JFrame("Cookie Chaser");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel mainPanel = new JPanel();
counterLabel = new JLabel(" ");
mainPanel.add(counterLabel);
frame.add(mainPanel);
frame.setSize(300, 200);
frame.setVisible(true);
new Thread(new Animation(this, counter)).start();
}
public void setCounterLabel(String text) {
counterLabel.setText(text);
}
public class Counter {
private int counter;
public int getCounter() {
return counter;
}
public void setCounter(int counter) {
this.counter = counter;
}
public void incrementCounter() {
this.counter++;
}
}
public class Animation implements Runnable {
private Counter counter;
private CookieChaser cookieChaser;
public Animation(CookieChaser cookieChaser, Counter counter) {
this.cookieChaser = cookieChaser;
this.counter = counter;
}
#Override
public void run() {
while (true) {
counter.incrementCounter();
repaint();
sleep(1000L);
}
}
private void repaint() {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
cookieChaser.setCounterLabel(Integer.toString(counter
.getCounter()));
}
});
}
private void sleep(long duration) {
try {
Thread.sleep(duration);
} catch (InterruptedException e) {
}
}
}
}
I'm changing "views" with cardLayout (this class has a JFrame variable). When a user clicks a new game button this happens:
public class Views extends JFrame implements ActionListener {
private JFrame frame;
private CardLayout cl;
private JPanel cards;
private Game game;
public void actionPerformed(ActionEvent e) {
String command = e.getActionCommand();
if (command.equals("New game")) {
cl.show(cards, "Game");
game.init();
this.revalidate();
this.repaint();
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
game.loop();
}
});
}
}
}
Game's loop method and heading of class:
public class Game extends JPanel implements KeyListener {
public void loop() {
while (player.isAlive()) {
try {
this.update();
this.repaint();
// first class JFrame variable
jframee.getFrame().repaint();
// first class JFrame variable
jframee.getFrame().revalidate();
Thread.sleep(17);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public void update() {
System.out.println("updated");
}
}
I'm painting using paintComponent()
public void paintComponent(Graphics g) {
System.out.println("paint");
...
}
Actually it's not painting anything. When I do not call loop() method (so it paints it just once) all images are painted correctly. But when I call loop() method, just nothing is happening in the window. (Even close button on JFrame doesn't work.)
How to fix that? (When I was creating JFrame inside game class everything worked fine, but now I want to have more views so I need JFrame in other class.)
Thanks.
Precursor: The Event Dispatch Thread (EDT).
Swing is single-threaded. What does this mean?
All processing in a Swing program begins with an event. The EDT is a thread that processes these events in a loop along the following lines (but more complicated):
class EventDispatchThread extends Thread {
Queue<AWTEvent> queue = ...;
void postEvent(AWTEvent anEvent) {
queue.add(anEvent);
}
#Override
public void run() {
while (true) {
AWTEvent nextEvent = queue.poll();
if (nextEvent != null) {
processEvent(nextEvent);
}
}
}
void processEvent(AWTEvent theEvent) {
// calls e.g.
// ActionListener.actionPerformed,
// JComponent.paintComponent,
// Runnable.run,
// etc...
}
}
The dispatch thread is hidden from us through abstraction: we generally only write listener callbacks.
Clicking a button posts an event (in native code): when the event is processed, actionPerformed is called on the EDT.
Calling repaint posts an event: when the event is processed, paintComponent is called on the EDT.
Calling invokeLater posts an event: when the event is processed, run is called on the EDT.
Everything in Swing begins with an event.
Event tasks are processed in sequence, in the order they are posted.
The next event can only be processed when the current event task returns. This is why we cannot have an infinite loop on the EDT. actionPerformed (or run, as in your edit) never returns, so the calls to repaint post paint events but they are never processed and the program appears to freeze.
This is what it means to "block" the EDT.
There are basically two ways to do animation in a Swing program:
Use a Thread (or a SwingWorker).
The benefit to using a thread is that the processing is done off the EDT, so if there is intensive processing, the GUI can still update concurrently.
Use a javax.swing.Timer.
The benefit to using a timer is that the processing is done on the EDT, so there is no worry about synchronization, and it is safe to change the state of the GUI components.
Generally speaking, we should only use a thread in a Swing program if there's a reason to not use a timer.
To the user, there is no discernible difference between them.
Your call to revalidate indicates to me that you are modifying the state of the components in the loop (adding, removing, changing locations, etc.). This is not necessarily safe to do off the EDT. If you are modifying the state of the components, it is a compelling reason to use a timer, not a thread. Using a thread without proper synchronization can lead to subtle bugs that are difficult to diagnose. See Memory Consistency Errors.
In some cases, operations on a component are done under a tree lock (Swing makes sure they are thread-safe on their own), but in some cases they are not.
We can turn a loop of the following form:
while ( condition() ) {
body();
Thread.sleep( time );
}
in to a Timer of the following form:
new Timer(( time ), new ActionListener() {
#Override
public void actionPerformed(ActionEvent evt) {
if ( condition() ) {
body();
} else {
Timer self = (Timer) evt.getSource();
self.stop();
}
}
}).start();
Here is a simple example demonstrating animation both with a thread and a timer. The green bar moves cyclically across the black panel.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class SwingAnimation implements Runnable{
public static void main(String[] args) {
SwingUtilities.invokeLater(new SwingAnimation());
}
JToggleButton play;
AnimationPanel animation;
#Override
public void run() {
JFrame frame = new JFrame("Simple Animation");
JPanel content = new JPanel(new BorderLayout());
play = new JToggleButton("Play");
content.add(play, BorderLayout.NORTH);
animation = new AnimationPanel(500, 50);
content.add(animation, BorderLayout.CENTER);
// 'true' to use a Thread
// 'false' to use a Timer
if (false) {
play.addActionListener(new ThreadAnimator());
} else {
play.addActionListener(new TimerAnimator());
}
frame.setContentPane(content);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
abstract class Animator implements ActionListener {
final int period = ( 1000 / 60 );
#Override
public void actionPerformed(ActionEvent ae) {
if (play.isSelected()) {
start();
} else {
stop();
}
}
abstract void start();
abstract void stop();
void animate() {
int workingPos = animation.barPosition;
++workingPos;
if (workingPos >= animation.getWidth()) {
workingPos = 0;
}
animation.barPosition = workingPos;
animation.repaint();
}
}
class ThreadAnimator extends Animator {
volatile boolean isRunning;
Runnable loop = new Runnable() {
#Override
public void run() {
try {
while (isRunning) {
animate();
Thread.sleep(period);
}
} catch (InterruptedException e) {
throw new AssertionError(e);
}
}
};
#Override
void start() {
isRunning = true;
new Thread(loop).start();
}
#Override
void stop() {
isRunning = false;
}
}
class TimerAnimator extends Animator {
Timer timer = new Timer(period, new ActionListener() {
#Override
public void actionPerformed(ActionEvent ae) {
animate();
}
});
#Override
void start() {
timer.start();
}
#Override
void stop() {
timer.stop();
}
}
static class AnimationPanel extends JPanel {
final int barWidth = 10;
volatile int barPosition;
AnimationPanel(int width, int height) {
setPreferredSize(new Dimension(width, height));
setBackground(Color.BLACK);
barPosition = ( width / 2 ) - ( barWidth / 2 );
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
int width = getWidth();
int height = getHeight();
int currentPos = barPosition;
g.setColor(Color.GREEN);
g.fillRect(currentPos, 0, barWidth, height);
if ( (currentPos + barWidth) >= width ) {
g.fillRect(currentPos - width, 0, barWidth, height);
}
}
}
}
What does update do? You probably shouldnt call game.loop() on the EDT. You are running a loop on EDT, your repaint wont ever be invoked since repaint queues an event on EDT and it seems kind busy. Try moving game.loop() to another thread
new Thread(new Runnable() {
#override
public void run() {
game.loop();
}
}).start();
This way you wont block the EDT while the repaint still gets to be executed on the EDT.
Move game.loop() method invocation to something like:
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
game.loop()
}
});
Thanks.
I want to call another applet by clicking a button; the old applet will then be closed or reloaded to the new applet.
My Action Listener doesn't have anything yet.
public class ConImage extends JApplet implements ActionListener {
Button btn;
Applet second;
public void init()
{
setSize(1600,900);
setLayout(null);
btn=new Button("Replace with other applet");
add(btn);
btn.addActionListener(this);
}
public void paint(Graphics g)
{
super.paint(g);
btn.setLocation(100, 100);
btn.setSize(100, 50);
}
public void actionPerformed(ActionEvent e)
{ second=null;
second= getAppletContext().getApplet("SecondClass");
if (second!=null)
{
if(e.getSource()==Time)
{
SecondClass ma= (SecondClass) second;
}
}
}
}
I'm pretty sure this isn't possible because of Java's security system. The best way to so it is to have a master class, which has an array of JApplet. On that master applet I would create a method that sets the visible applet from the array, calls init() and when a render is requested call paint() of that applet.
Like so:
public class MasterApplet extends JApplet {
private int index = 0;
private JApplet[] applets;
public void init(){
JApplet appletA = new AppletA();
JApplet appletB = new AppletB();
applets = new JApplet[]{appletA, appletB};
setViewing(index);
}
public void paint(Graphics g){
applets[index].paint(g);
}
public void setViewing(int idex){
index = idex;
applets[idex].init();
revalidate();
repaint();
}
Pretty much if you want to change the applet add it to the array of applets, and then call setViewing() with the index of that applet.
I need to run a background thread in my Java GUI that only runs when I click a button and pauses when I click that button again. I am not exactly sure how to set this up, but I have placed a thread in my constructor and the while loop within is set to go through when I set a specific boolean to TRUE. One button switches from setting this boolean TRUE or FALSE.
Everything else I have in this GUI works fine. When I tried debugging the thread, it actually works as I step through the thread but nothing when I try running the GUI completely. The GUI is rather large so I'm gonna put up a portion of the constructor and the action listener of the button. The rest of the code is unnecessary since it works just fine. I need to know what I am doing wrong here:
public BasketballGUI() {
// certain labels and buttons
Thread runningSim = new Thread() {
public void run() {
while(simRun) {
// do stuff here
}
}
};
runningSim.start();
}
// other GUI stuff
// actionListener that should run the thread.
class SimButtonListener implements ActionListener {
public void actionPerformed(ActionEvent arg0) {
if(!simRun) {
simRun = true;
sim.setText("Pause Simulator");
}
else if(simRun) {
simRun = false;
sim.setText("Run Simulator");
}
// other stuff in this actionListener
}
}
Establish a Swing based Timer with an ActionListener that will be called repeatedly.
In the actionPerformed(ActionEvent) method call repaint().
Start the timer (Timer.start()) when the user clicks Start
Stop the timer (Timer.stop()) when the user clicks Stop
If you cannot get it working from that description, I suggest you post an SSCCE of your best attempt.
I thought I had one 'lying around'.. Try this working SSCCE which uses images created in this SSCCE.
I could see this background thread useful for a Java GUI when handling button events to affect something like a text area or progress bar.
For the sake of argument, I will build you a tiny GUI that affects a Text Area. I hope this helps you.
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.concurrent.atomic.AtomicBoolean;
import javax.swing.*;
public class TestClass extends JPanel {
super("TestClass - Title");
private AtomicBoolean paused;
private JTextArea jta;
private JButton btn;
private Thread thread;
public TestClass() {
paused = new AtomicBoolean(false);
jta = new JTextArea(100, 100);
btn = new JButton();
initialize();
}
public void initialize() {
jta.setLineWrap(true);
jta.setWrapStyleWord(true);
add(new JScrollPane(jta));
btn.setPreferredSize(new Dimension(100, 100));
btn.setText("Pause");
btn.addActionListener(new ButtonListener());
add(btn);
Runnable runnable = new Runnable() {
#Override
public void run() {
while(true) {
for(int i = 0; i < Integer.MAX_VALUE; i++) {
if(paused.get()) {
synchronized(thread) {
try {
thread.wait();
} catch(InterruptedException e) {
}
}
}
}
jta.append(Integer.toString(i) + ", ");
try {
Thread.sleep(500);
} catch (InterruptedException e) {
}
}
}
};
thread = new Thread(runnable);
thread.start();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(100, 30);
}
class ButtonListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent event) {
if(!paused.get()) {
btn.setText("Start");
paused.set(true);
} else {
btn.setText("Pause");
paused.set(false);
synchronized(thread) {
thread.notify();
}
}
}
}
}
Main class to call everything.
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
public class MainClass {
public static void main(final String[] arg) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new TestClass());
frame.pack();
frame.setVisible(true);
frame.setLocationRelativeTo(null);
}
});
}
}
I did not test this code to see if it works exactly, Its main goal is to break you through your coders block and use my components to fix your issue. Hope this helped. Need anything else Email me at DesignatedSoftware#gmail.com
I have made an applet name ParentApplet.java whose task is to create a child frame
Child frame coding is defined in ChildFrame.java
ParentApplet.java
public class ParentApplet extends Applet {
ChildFrame frame;
private static int time = 0;
#Override
public void start() {
frame.setVisible(true);
}
#Override
public void stop() {
frame.setVisible(false);
}
#Override
public void init() {
frame = new ChildFrame("Child");
this.setSize(400, 400);
}
#Override
public void paint(Graphics g) {
g.drawString("Child's Info : " + (++time), 50, 100);
g.drawString(frame.getMessage(), 400, 100);
System.out.println(frame.getMessage().isEmpty() ? "Empty" : frame.getMessage());
}
}
ChildFrame.java
public class ChildFrame extends Frame {
private String mess = "";
public ChildFrame(String title) {
super(title);
addMouseListener(new MyMouseAdapter(this));
addWindowListener(new MyWindowAdapter(this));
setSize(300, 500);
}
public String getMessage() {
return mess;
}
public void setMessage(String mess) {
this.mess = mess;
(new ParentApplet()).repaint();
System.out.println("Click");
}
}
MyMouseAdapter.java
public class MyMouseAdapter extends MouseAdapter {
ChildFrame frame;
public MyMouseAdapter(ChildFrame frame) {
this.frame = frame;
}
#Override
public void mouseClicked(MouseEvent e) {
frame.setMessage("Mouse Cliked in Child");
}
}
MyWindowAdapter.java
public class MyWindowAdapter extends WindowAdapter {
ChildFrame frame;
public MyWindowAdapter(ChildFrame frame) {
this.frame = frame;
}
#Override
public void windowClosing(WindowEvent we) {
frame.setVisible(false);
}
}
Now i am unable to reach the paint method again even after calling the repaint method from the ChildFrame class. Please suggest me whether i have done something wrong or some thing i need to understand.
Thanks in advance
Gagandeep Singh
The answer to your question is basically "you don't do that".
The Applet's paint() method is responsible for painting the contents of the actual applet component-- i.e. the visible component that appears in the web page. Your ChildFrame should then have a separate paint() method to paint itself (or in fact, would usually have a Canvas added to it, and that Canvas in turn has its own paint() method).
(Remember that in Java a "Frame" is effectively a "window"-- i.e. a standalone window that opens separately to the web page.)
You can call repaint() on whatever component from wherever you like. This will eventually lead to that component's paint() method being called. In your particular example, you shouldn't call "new ParentApplet()" -- you don't want to call repaint() on some randomly created new applet, but rather on the single already existing one. So change this by passing a reference to your applet into the constructor of ChildFrame which ChildFrame can then hold as an instance variable and re-use when needed:
public class ChildFrame extends Frame {
private String mess = "";
private final ParentApplet parentApplet;
public ChildFrame(ParentApplet applet, String title) {
super(title);
this.parentApplet = applet;
addMouseListener(new MyMouseAdapter(this));
addWindowListener(new MyWindowAdapter(this));
setSize(300, 500);
}
...
public void setMessage(String mess) {
this.mess = mess;
parentApplet.repaint();
}
}
I must admit that so far, it's not immediately obvious why you would have a setMessage() on a separate frame whose purpose is to set the message displayed in the applet. Why not put the setMessage() method on the applet in that case? But maybe you have another reason for doing it your way that isn't apparent so far.