Develop Reference

Creating and Discarding JFrames that run Threads

I'm writing my Tetris using Java Swing. The Game class revolves around a JFrame (frame), which consists of a TetrisPanel extending JPanel (panel) where the blocks fall, a JLabel (pontok) point counter, a JTextArea (rekord_text) showing high scores, and another JPanel (kovi) showing the next block to fall. My idea is that the game has 3 difficulty levels, where the blocks fall with different speed.
I thought the best way of approaching this problem is to create a new JFrame with the components above, but with the blocks' speed set different. I am able to close the old JFrame. However, when the new JFrame opens up, it is only a blank frame, and it won't respond to closing the window.
I should add that TetrisPanel is running a thread, but I am 90% sure I stop that with a volatile boolean.
Constructor of the Game class:
this.difSet(nehezseg); //this function sets the falling velocity
TetrisPanel.stopped = true; //this static member is the volatile boolean responsible for stopping the thread
new_game = false;
frame = new JFrame("Tetris_alpha");
frame.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
panel = new TetrisPanel();
TetrisPanel.stopped = false;
new Thread(panel).start();
frame.add(panel, c);
pontok = new JLabel ("0");
frame.add(pontok, c);
rekord_text = new JTextArea();
//i set up the area
frame.add(rekord_text, c);
kovi = new NextAktualPanel();
frame.add(kovi, c);
menu = new MyMenu(this);
frame.setJMenuBar(menu);
frame.addWindowListener(new WindowAdapter()
{
#Override
public void windowClosing(WindowEvent e)
{
rekordok.add(panel.getPont());
rekordok.write(f);
e.getWindow().dispose();
System.exit(0);
}
}
);
frame.pack();
frame.setVisible(true);
}
The Game.start() function containing the game loop:
public void start()
{
//game_loop
while (!panel.GameOver() && !new_game)
{
if (panel.aktualLeertDetector())
{
panel.addAktualToBlocks();
panel.addNewAktual(next);
Elem temp = new Elem(0,0,rand.nextInt(7));
while (temp.getTipus() == next.getTipus())
temp = new Elem(0,0,rand.nextInt(7));
next = temp;
kovi.setNextAktual (next);
}
if (!paused)
pontok.setText(Integer.toString(panel.getPont()));
kovi.repaint();
panel.repaint();
}
The function which opens the new frame:
Public void newGame (Game g)
{
Game.new_game = true;
g.frame.dispose();
Game new_game = new Game("easy");
g = new_game;
g.start();
}
And the run() function of TetrisPanel:
public static volatile boolean stopped = false;
#Override
public void run() {
while (!stopped)
{
aktual.zuhan();
this.sorTeleAction();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
Any help would be appreciated, including ideas about different a approach.

Do not use volatile boolean as status variable, use AtomicBoolean instead, volatile it's not the correct way to do this kind of things, and it does not either cause "immediate variable updating"... this is not volatile purpose.
It's not a good idea to start a thread on main AWT thread, you still have to use SwingUtilities.invokeLater(Runnable runnableAction). You can use something like this when launching a Gui Thread:
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
try {
new Thread(threadAction).start();
} catch (Exception e) {
}
}
});
Hope that this will solve you problem!

JFrame: Sleep between statements

I'm still very new to the world of programming and have recently noticed, that whenever I tell the programm to idle for some seconds between the code, it instead sleeps at the start and then goes through the remaining code.
I've tried various ways like thread.sleep() or Timers but I never get what I want.
Here is an example:
public void Console(){
Console.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
Console.setSize(500, 500);
Console.setLocationRelativeTo(null);
Console.setResizable(false);
Console.setVisible(true);
Console.setTitle("Console");
JPanel contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
Console.setContentPane(contentPane);
contentPane.setLayout(null);
contentPane.setBackground(new Color(47, 79, 79));
cinput.setBounds(10, 442, 353, 20);
contentPane.add(cinput);
cinput.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
in();
cinput.requestFocus();
}
});
cinput.setColumns(10);
cinput.requestFocus();
JButton Enter = new JButton("Enter");
Enter.setBounds(373, 439, 111, 23);
contentPane.add(Enter);
JScrollPane scrollPane = new JScrollPane();
scrollPane.setBounds(10, 10, 474, 421);
contentPane.add(scrollPane);
cmd.setEditable(false);
cmd.setFont(new Font("Courier New", Font.PLAIN, 18));
cmd.setForeground(Color.GREEN);
cmd.setText("CONSOLE\n");
cmd.setBackground(Color.BLACK);
cmd.setLineWrap(true);
cmd.setWrapStyleWord(true);
scrollPane.setViewportView(cmd);
Enter.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
in();
cinput.requestFocus();
}
});
}
private void addText(JTextArea textArea, String text) {
String input = textArea.getText();
String output = input + text;
textArea.setText(output);
}
private void in()
{
String input = cinput.getText();
cinput.setText("");
String text;
text = input;
addText(cmd, "> " + text + "\n");
if(text.equals("start"))
{
addText(cmd, "1");
// SLEEP HERE
Thread.sleep(1000);
// -------------------
addText(cmd, "2");
}
else if(text.equals("exit"))
{
Console.dispose();
}
}
It should look something like this:
In this very basic 'Console', whenever I type 'start' in the textbox and hit enter, I want the number '1' to appear first and after 1000 mseconds the number '2' should appear, which it doesn't!
Is there any way to tell the programm to sleep between statements instead of always sleeping at the beginnig of the function?
Thanks in advance

While technically the answers above are true, your problem is
You must do all Swing work on the Swing Event Dispatch Thread.
You really, really, don't want to sleep the main Swing Event Dispatch Thread!
What you want to do instead is create a helper class that wraps the javax.swing.Timer (NOT the java.util.timer) that allows you to easily run code on the event thread after a certain number of milliseconds has passed.
public abstract class LazyAction implements Runnable {
public LazyAction(int millis) {
Timer t = new Timer(millis, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
try{
LazyAction.this.run();
catch(Exception e){
//Your error handling code
}
}
});
t.setRepeats(false);
t.start();
}}
Now, to use this code, you then call it by:
addText(cmd, "1");
new LazyAction(300){
#Override
public void run() {
addText(cmd, "2");
}
}
(Note if you are using Java 8 you could use Lambdas instead, in that case LazyAction would take in a Runnable rather than implementing Runnable...)

It looks like you are trying to put to sleep the main Thread which is not the best idea. Run your own Thread and put it to sleep.
Try this:
System.out.println(1);
SwingUtilities.invokeLater(() -> {
new Timer(1000, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
System.out.println(2);
}
}).start();
});
You can also do this without Thread.sleep():
long tick = 1000;
long startTime = System.currentTimeMillis();
while (true) {
long now = System.currentTimeMillis();
while (now - startTime > tick) {
System.out.println("Seconds from start time: " + (int) (tick / 1000));
tick += 1000;
}
}
If it suites you just tweak the above example for your needs(it also accounts for possible lag so the number of seconds will still be correct).

Put a sleep statement before adding the first line of text:
Thread.sleep(1000);
addText(cmd, "1");
// SLEEP HERE
Thread.sleep(1000);
// -------------------
addText(cmd, "2");

Why my GUI won't update even tho repaint() is being called?

I am having some difficulties using swing workers, timers, and I am actually a little confused.
As far as my understanding goes, I have to put on a timer to set-up recurring tasks that have to be called by the EDT.
I'm trying to make a program that shows graphically a sorting alghoritm (like this : https://www.youtube.com/watch?v=kPRA0W1kECg )
I just don't understand why the GUI won't refresh. I am quite sure the repaint method is being called since I put a sysout showing me the ordered values and it seems to work , but the GUI just... doesn't change.
Here's my code:
public class MainWindow {
private JFrame frame;
JPanel panel;
public final static int JFRAME_WIDTH = 800;
public final static int JFRAME_HEIGHT = 600;
public final static int NELEM = 40;
ArrayList<Double> numbers;
ArrayList<myRectangle> drawables = new ArrayList<myRectangle>();
Lock lock = new ReentrantLock();
Condition waitme = lock.newCondition();
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
MainWindow window = new MainWindow();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
public MainWindow() {
initialize();
}
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, JFRAME_WIDTH + 20, JFRAME_HEIGHT + 40);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panel = new myPanel();
frame.getContentPane().add(panel, BorderLayout.CENTER);
Timer timer = new Timer(500, new ActionListener() {
#Override
public void actionPerformed(ActionEvent arg0) {
lock.lock();
try{
//Updating the gui
panel.repaint();
panel.revalidate();
//Giving the OK to the sorting alghoritm to proceed.
waitme.signal();
}catch(Exception e){
e.printStackTrace();
}finally{
lock.unlock();
}
}
});
timer.start();
SwingWorker<Integer, String> sw = new SwingWorker<Integer, String>(){
#Override
protected Integer doInBackground() throws Exception {
mapAndCreate();
bubbleSort();
return null;
}
};
sw.execute();
}
private void bubbleSort() throws InterruptedException{
for(int i=0; i < NELEM; i++){
for(int j=1; j < (NELEM-i); j++){
if(drawables.get(j-1).wid > drawables.get(j).wid){
//swap the elements!
myRectangle temp = drawables.get(j-1);
drawables.set(j-1, drawables.get(j));
drawables.set(j, temp);
lock.lock();
try{
//Wait for the GUI to update.
waitme.await();
}catch(Exception e){
e.printStackTrace();
}finally{
lock.unlock();
}
}
}
}
}
/***
* Function that maps values from 0 to 1 into the rectangle width.
*/
private void mapAndCreate() {
double max = 0;
numbers = new ArrayList<Double>(NELEM);
//Finding maximum.
for(int i = 0; i < NELEM; i++){
Double currElem = Math.random();
if(currElem > max) max = currElem;
numbers.add(currElem);
}
//Mapping process
int offset = 0;
for(int j = 0; j < NELEM; j++){
Integer mapped = (int) (( JFRAME_WIDTH * numbers.get(j) ) / max);
myRectangle rect = new myRectangle(offset , mapped);
drawables.add(rect);
offset += JFRAME_HEIGHT / NELEM;
}
}
private class myRectangle{
int myy , wid , colorR,colorG,colorB;
public myRectangle(int y , int wid){
this.myy = y;
this.wid = wid;
Random r = new Random();
colorR = r.nextInt(255);
colorG = r.nextInt(255);
colorB = r.nextInt(255);
}
}
private class myPanel extends JPanel{
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
for(myRectangle rectan : drawables){
Graphics2D graphics2D = (Graphics2D)g;
System.out.println(rectan.wid);
Rectangle2D.Double rect = new Rectangle2D.Double(0,rectan.myy,rectan.wid,JFRAME_HEIGHT / NELEM);
graphics2D.setColor(new Color(rectan.colorR,rectan.colorG,rectan.colorB));
graphics2D.fill(rect);
}
System.out.println("====================================================================================================");
}
}
}

Most OSs (or rather the UI frameworks which they use) don't support concurrent access. Simply put, you can't render two strings of text at the same time.
That's why Swing runs all rendering operations in the UI thread. Calling rendering functions (like paint()) outside of the UI thread can cause all kinds of problems. So when you do it, Swing will just remember "I should repaint" and return (instead of doing any actual work). That way, Swing protects you but most people would prefer to get an error with a useful message.
A timer always also means that there is a thread somewhere which executes when the timer runs out. This is not the UI thread of Swing. So any paing operations there must be wrapped with EventQueue.invokeLater() or similar.
Another common bug is to hog the UI thread (so no rendering happens because you do complex calculations there). That's what the SwingWorker is for. Again, in most methods of the SwingWorker, calling methods which would render something is forbidden (-> use invokeLater()).
So my guess is that the UI thread waits for the lock and the lock simply isn't unlocked early or often enough. See this demo how to do a simple animation in Swing.
public class TimerBasedAnimation extends JPanel implements ActionListener {
public void paint(Graphics g) {
// setup
// do some first-run init stuff
// calculate the next frame
// render frame
}
public void actionPerformed(ActionEvent e) {
repaint();
}
public static void main(String[] args) {
JFrame frame = new JFrame("TimerBasedAnimation");
frame.add(new TimerBasedAnimation());
...
}
}
As you can see in the code doesn't lock. Instead, you just send "render now" events from actionPerformed to Swing. Some time later, Swing will call paint(). There is no telling (and no way to make sure or force Swing) when this will happen.
So good animation code will take the current time, calculate the animation state at that time and then render it. So it doesn't blindly step through N phases in M seconds. Instead, it adjusts for every frame to create the illusion that the animation is smooth when it really isn't.
Related:
Java: Safe Animations with Swing
How to Use Swing Timers

How to display a Swing timer's remaining time in one second intervals?

I've been working on a simple game using a Java Applet in which the player's goal is to get as many points as possible within a 30 second timeframe. Right now, I'm using a Swing timer to count down from 30 seconds, and once the 0 mark is reached, a "game over" screen is displayed with the player's score. I have these instance variables:
ActionListener listener = new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
screenState = 0;
repaint();
}
};
Timer displayTimer = new Timer(30000, listener);
When the player clicks the "play" button, I execute displayTimer.start();.
Then, I have this within the appropriate case in my paint class:
g.drawString("Time Remaining: " + displayTimer.getDelay()/1000, 650, 100);
So, obviously, right now it's just displaying a static "Time Remaining: 30", and the screens switches after 30 seconds. What I'm trying to figure out is how I can repaint this value every one second so that it's a live timer. The only help I've been able to find thus far is for people use components.

ActionListener listener = new ActionListener() {
int count = 0;
#Override
public void actionPerformed(ActionEvent e) {
if (count++==30) {
screenState = 0;
}
repaint();
}
};
Timer displayTimer = new Timer(1000, listener); // make it 30 times faster

You can use the a Thread that sleep it every one second using the sleep method of it
Here is a little sample that count to 30 with 1 second interval
public static void main(String[] args) {
Thread t = new Thread(new Runnable() {
#Override
public void run() {
int count = 0;
while(true)
{
if(count == 30) //end at 30 second
break;
try {
Thread.sleep(1000);
System.out.println("updated");
++count;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
});
t.start();
}

Java Swing Concurrency display JTextArea

I need to execute/display a series of events from a Arraylist to a JTextArea, however, each Event gets execute with different time. Following is a quick example of my goal:
public void start(ActionEvent e)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
jTextArea.append("Test" + "\n");
try
{
Thread.sleep(3000);
} catch (InterruptedException e1)
{
e1.printStackTrace();
}
jTextArea.append("Test1" + "\n");
}
});
}
So right now, "Test" and "Test1" display on JTextArea after whole execution is completed.
How do I make "Test" display first, then 3 secs later, display "Test1"
Thank u all in advance

invokeLater schedules the runnable to run on the Event Dispatch Thread. You shouldn't sleep within it or you will starve the dispatch thread. Try using a separate worker thread instead:
Thread worker = new Thread(new Runnable(){
public void run(){
jTextArea.append("Test" + "\n");
try {
Thread.sleep(3000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
jTextArea.append("Test1" + "\n");
}
});
worker.start();

If your tasks are time/cpu intensive, then yes, definitely use a background thread to do this such as a SwingWorker object or a Runnable run in a Thread. If however what you need to do is to stagger the display of something and all you are looking for is the Swing equivalent of Thread.sleep(3000), then your best option is to use a Swing Timer. There is an excellent tutorial on how to use these which you can find here: http://download.oracle.com/javase/tutorial/uiswing/misc/timer.html
For example:
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class Fu extends JPanel {
private static final int TIMER_DELAY = 600;
protected static final int MAX_COUNT = 20;
private JTextArea jTextArea = new JTextArea(10, 10);
private JButton startBtn = new JButton("Start");
private Timer timer;
public Fu() {
startBtn.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
startAction(e);
}
});
add(new JScrollPane(jTextArea, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED));
add(startBtn);
}
private void startAction(ActionEvent e) {
if (timer != null && timer.isRunning()) {
// prevent multiple instances of timer from running at same time
return;
}
timer = new Timer(TIMER_DELAY, new ActionListener() {
private int count = 0;
public void actionPerformed(ActionEvent e) {
if (count < MAX_COUNT) {
count++;
jTextArea.append("Test " + count + "\n");
} else {
jTextArea.append("Done! \n");
timer.stop();
timer = null;
}
}
});
timer.setInitialDelay(0);
timer.start();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JFrame frame = new JFrame("Foo");
frame.getContentPane().add(new Fu());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
}

As pointed out, this is a bad idea, as you will block the event thread.
However, understanding the reason for this is important as well. As you seem to know, all code that affects the state of Swing components needs to happen in the event handling thread (which is the reason why invokeLater and friends should always be used).
What is a bit less better known is that paining code also executes in the event handling thread. When your call to Thread.sleep is executing, it's not only blocking the event thread, it's also blocking any painting of components. This is why the full update appears to happen in one go -- the JTextArea is updated but it can't be repainted until your run method returns.
Lots of info available here: http://java.sun.com/products/jfc/tsc/articles/threads/threads1.html