I have some doubts about the use of the methods wait() and notify(). I have the next code which has some button events, the first time the user pushes the button it has to stop printing, and the second time it restarts printing again. I understand that is better to use Runnable instead of Thread, but I have to use Thread because of the requirements. The code works fine the first time the button is pushed but the second time it doesn´t, I want to use the wait() and the notify, but i don´t know how to do it with this particular code.
class Thr extends Thread{
private int count = 0;
private long pause;
private boolean canPrint = true;
private JTextArea textArea;
Thr(long miliseconds,JTextArea text){
pause = miliseconds;
textArea = text;
}
public void pushedButton(){
if(canPrint)
this.canPrint = false;
else
this.canPrint = true;
}
public void run()
{
while(this.canPrint)
{
try
{
this.printCounter();
Thread.sleep(pause);
this.count++;
}
catch(InterruptedException e)
{
e.printStackTrace();
}
}
}
public void printCounter(){
String time;
time = Integer.toString(count);
textArea.setText(time);
}
}
class Interface extends JFrame implements ActionListener{
private JTextArea textArea,textArea2;
private JButton button;
private Thr thread,threadEvent;
Interface()
{
textArea = new JTextArea(10,7);
textArea2 = new JTextArea(10,7);
thread = new Thr(2000,textArea);
threadEvent = new Thr(1000,textArea2);
button = new JButton("Pausar/Reanudar");
this.getContentPane().add(button,BorderLayout.SOUTH);
this.getContentPane().add(textArea,BorderLayout.WEST);
this.getContentPane().add(textArea2,BorderLayout.EAST);
thread.start();
threadEvent.start();
button.addActionListener(this);
}
public void actionPerformed(ActionEvent event)
{
threadEvent.pushedButton();
}
}
public class MensajesHilos {
public static void main(String[] args){
Interface i = new Interface();
i.setTitle("Control Threads");
i.setBounds(200, 200, 300, 240);
i.setVisible(true);
}
}
The way you have coded, if you want to achieve the desired result,
I feel the modification need to be done in run method,
public void run()
{
while(true)
{
if(this.canPrint){
try
{
this.printCounter();
Thread.sleep(pause);
this.count++;
}
catch(InterruptedException e)
{
e.printStackTrace();
}
}
}
}
in this way, your Thread will never go dead and toggle printing based on canPrint boolean value.
Also, make sure to declare canPrint variable volatile, so that changes to it will be directly written to main memory and reflected immediately.
"button event doesn´t work properly"
This is false, if you put a print statement in the actionPerformed method, you will see that it is called every time you press the button.
By the way note that you can simplify this
if(canPrint)
this.canPrint = false;
else
this.canPrint = true;
To
this.canPrint = !this.canPrint;
Note that it is a good practice to always put #Override anotation on top of overriden method.
#Override
public void actionPerformed(ActionEvent event)
{
threadEvent.pushedButton();
}
Now why don't you get the expected result ?
You ommit to call thread.pushedButton, so the canPrint will only be reseted in the threadEvent object, and will never be in thread.
Note that once the boolean are set to false, you will exit the loop and the process won't start back after even if you re-set the boolean value to true. This example will works using while(true) however, you should change the true to any sentinel value to handle the exit of the program as this will loop forever.
#Override
public void run()
{
while(true)
{
if(this.canPrint)
{
this.printCounter();
this.count++;
}
try
{
Thread.sleep(pause);
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
Also, make sure that pause is never 0 else you will eat all of the computer process.
Note that, as other stated, you should declare variables that are accessed in thread as volatile (canPrint) in your case.
Related
I have a question about using events to run loops since doing so seems to lock down the thread. For example I have an nativeMousePressed and nativeMouseReleased event and I am trying to execute some code continuously while the mouse is pressed and then stop when its released. I tried to do this by creating a static boolean variable in another manager class and then setting it to true when the mouse is being pressed and false when the mouse is released. Then I decided to make a while loop that gets called from inside that nativeMousePressed event that uses the boolean value I talked about earlier. The issue is that no events can be called while that while loop is running which means the boolean value when never become false creating an infinite loop. How can I run the while loop while keeping the events running as well?
I assume this has to do with the thread being locked down but I have not worked with stuff like this much and would like some help figuring out how to run both these things in parallel.
public class NativeMouseEvent implements NativeMouseListener {
Program program = new Program();
#Override
public void nativeMouseClicked(org.jnativehook.mouse.NativeMouseEvent e) {
}
#Override
public void nativeMousePressed(org.jnativehook.mouse.NativeMouseEvent e) {
if(e.getButton() == 1 && Controller.threeClicked) {
Controller.fixAim = true;
program.start();
}
}
#Override
public void nativeMouseReleased(org.jnativehook.mouse.NativeMouseEvent e) {
program.interrupt();
Controller.fixAim = false;
}
}
Here is what my second thread is running...
public class Program extends Thread {
public void run() {
while(Controller.fixAim) {
System.out.println("test");
}
}
Here my second attempt which also gives me an error saying that this.program is null.
public class NativeMouseEvent implements NativeMouseListener {
Program program;
#Override
public void nativeMouseClicked(org.jnativehook.mouse.NativeMouseEvent e) {
}
#Override
public void nativeMousePressed(org.jnativehook.mouse.NativeMouseEvent e) {
if(e.getButton() == 1 && Controller.threeClicked) {
Controller.fixAim = true;
if(program != null) {
program = new Program();
program.start();
}
}
}
#Override
public void nativeMouseReleased(org.jnativehook.mouse.NativeMouseEvent e) {
program.interrupt();
program = null;
Controller.fixAim = false;
}
}
Start a tread on mouse down and stop the tread on mouse up. In the thread do circle drawing.
Something like below java code. Note: it is just an example. You need to make changes to make it work in your android environment.
public class Test {
Thread drawTask;
public void mouseDown() {
drawTask = new Thread(()-> {
int i = 0;
try {
for(;;) {
System.out.print("\rDrawing circle " + i++);
Thread.sleep(500);
}
} catch(InterruptedException e) {
System.out.println("finished drawing circle.");
}
});
drawTask.start();
}
public void mouseUp() {
if(drawTask != null) {
drawTask.interrupt();
drawTask = null; //<--- make sure you do this
}
}
public static void main(String[] args) {
Test test = new Test();
Scanner in = new Scanner(System.in);
System.out.println("type anything and press Enter to simulate mouse down/up");
in.next();
test.mouseDown();
in.next();
test.mouseUp();
in.next();
in.close();
}
}
I want to make an easy app. But I want to stop thread with a button. This code doesn't work. I saw all web sites like this way. I don't understand why not working.
Thread is starting with a btnStart.
btnStop isn't working. I wrote stopThread() function for stopping.
Which how this can do another way? Any idea?
private volatile boolean isRunning;
==============
private void stopThread() {
isRunning=false;
Thread.currentThread().interrupt();
}
==============
private final void runThread() {
new Thread() {
public void run() {
while (isRunning) {
try {
Random r = new Random();
islemler[0] = "+";
islemler[1] = "-";
islemler[2] = "*";
islemler[3] = "/";
for (int i = 0; i <10; i++) {
islem1 = islemler[r.nextInt(4)];
islem2 = islemler[r.nextInt(4)];
islem3 = islemler[r.nextInt(4)];
islem4 = islemler[r.nextInt(4)];
txt1.setText("1"+islem1+"1");
txt2.setText("1"+islem2+"1");
txt3.setText("1"+islem3+"1");
txt4.setText("1"+islem4+"1");
Thread.sleep(150);
Thread.sleep(50);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
}.start();
}
==============
btnStart.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
isRunning=true;
runThread();
**This part is working**
}
});
==============
btnStop = new JButton("Stop");
btnStop.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
stopThread();
**But this part is not working. Can you help??**
}
});
The Problem
You have two threads open, possibly three if you have one set aside for the ui.
The first thread is the one the program launches on, and the second would be where you creating the random object and for-loop. When you are calling "stop thread" you are doing so from either the main thread or the third thread for the ui.
This means that
Thread.currentThread().interrupt();
is not closing the correct thread.
The Solution
For a solution to this problem, look at this GeeksForGeeks article which suggests storing threads as a variable and then you can reliably call the interrupt method on it.
public class Worker extends SwingWorker<Integer, String> {
private JLabel screen;
public Worker(JLabel screen) {
this.screen = screen;
}
#Override
protected Integer doInBackground() throws Exception {
for (; ; ) {
publish(String.valueOf(Calendar.getInstance().getTimeInMillis()));
}
}
#Override
protected void process(List<String> chunks) {
screen.setText(chunks.get(0));
}
}
And in Form:
public class Form extends JPanel{
private JButton startButton;
private JPanel rootPanel;
private JButton stopButton;
private JLabel screen;
private Worker worker;
public Form() {
startButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
worker = new Worker(screen);
worker.execute();
}
});
stopButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
worker.cancel(true);
System.out.println(worker.isDone());
System.out.println(worker.isCancelled());
}
});
}
private void createUIComponents() {
rootPanel = this;
}
}
I tried to write same code with Tread, but it doesn't work too. And console output after click on stopButton:
true
true
So, worker have done, but program still continue show milliseconds. What is a post-death life? And in case of using Thread same thing: method isAlive() return "false".
Based on your code, it looks like you need a worker with a loop to keep running until the master thread tells it to stop running, which is done with worker.cancel(true);. The problem is that you are canceling it, but doing nothing to signal the loop itself to stop iterating. To fix this, you should change
for (; ; ) {
publish(String.valueOf(Calendar.getInstance().getTimeInMillis()));
}
to
while(!isCancelled()){
publish(String.valueOf(Calendar.getInstance().getTimeInMillis()));
}
Note the phrasing of 'isCancelled' from the java docs:
isCancelled()
Returns true if this task was canceled before it completed normally.
Since the loop never closes on its' own, it will never complete normally.
So I wrote a little program which will move circles around and when they collide they will move opposite direction, however when I'm trying to delay the execution so they won't move around stupidly fast I get java.lang.IllegalMonitorStateException
Lock in canvasRender.java, creating an instance:
ReentrantLock renderLock = new ReentrantLock();
Method which will pause execution for a moment, so circles won't move around super fast.
publlic void delay(){
renderLock.unlock();
try { Thread.sleep(10); } catch (Exception e) {} ;
renderLock.lock();
}
then from another class where I create a window and add actionListener
public static void main(String[] args){
//Buttons and other elements
// ...
JButton start = new JButton("Start!");
createAndShowGUI();
}
In createAndShowGUI():
static void createAndShowGUI(){
//adding elements to panels
start.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
start(); //this will set gameIsRunning variable to true and create models
while (gameIsRunning) {
//update(); //which has delay(); at the end of frame drawing
//but even if just put delay()
delay(); //still says exception
start.setEnabled(false); //while game is running button is unavailable
}
start.setEnabled(true);
}
});
}
In this case my lock is owned by the Thread main, but at the time when I click button 'Start!' current is Thread AWT-EventQueue-0, and so the program crashes. How to fix this issue? (or where am I silly?)
The problem is that you're calling renderLock.unlock() from AWT-EventQueue-0 after renderLock.lock() was called by main. The thread AWT-EventQueue-0 isn't allowed to call unlock() it, since it's not the thread that called lock() it in the first place.
You could probably simplify things by dropping ReentrantLock and just using synchronized.
I don't know the design of the rest of your program, but it seems to me that the contents of the while loop belong in a separate thread. You generally don't want to loop in a UI listener method (such as actionPerformed() in ActionListener) because it will freeze up the GUI.
One thing you could do is add an Object to synchronize on:
private static final Object LOCK = new Object()
Then move the game-updating logic to its own thread — something like this:
private static class GameThread extends Thread {
public GameThread() {
super("GameThread");
}
public void run() {
synchronized (LOCK) {
start();
while (gameIsRunning) {
update();
try {
// Try to sleep for 10 millis:
LOCK.wait(10);
} catch (InterruptedException ignored) { }
}
}
// Re-enable the button:
javax.swing.SwingUtilities.invokeLater(() -> start.setEnabled(true));
}
}
And you can change your ActionListener to simply disable the button and start a GameThread:
start.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
start.setEnabled(false);
synchronized(LOCK) {
if(!gameIsRunning) {
new GameThread().start();
}
}
}
});
Any other code that checks or modifies the state of the game should also be enclosed within a synchronized (LOCK) block. And if update() modifies the GUI as well as the game state, then it probably needs to do so with SwingUtilities.invokeLater().
It might also make things more clear to rename start() to setupGame() and JButton start to JButton startButton.
What I am trying to do is an Appled which throws 2 threads, each running a counter which increases itself via an infinite loop
I then use a while(true) in the Applet's paint() method, which continuously paints the counters, the problem is that I have also 2 buttons, each intended to stop each thread, but the infinite loop in the paint() method doesn't let me neither click none of them nor close the Applet's window nor anything
Here a screenshot followed by the code
btw I'm certain the problem is the paint() loop as if I disable the loop I can interact with the buttons, but the counters are obviously not updated, and weird thing is that I put the mouse cursor over the buttons to show it took the form like when you want to resize a windows but the imprpant didn't capture it :/
http://i.imgur.com/PJnDI4u.png
public class MainApplet extends Applet implements ActionListener {
private static final long serialVersionUID = -2500043816999861110L;
private Font fuente;
private Button bUno, bDos;
private HiloContador hUno, hDos;
public void init() {
setBackground(Color.LIGHT_GRAY);
fuente = new Font("Verdana",Font.BOLD,26);
bUno = new Button("Parar");
bUno.addActionListener(this);
bDos = new Button("Parar");
bDos.addActionListener(this);
bUno.setSize(40,20);
add(bUno);
bDos.setSize(40,20);
add(bDos);
hUno = new HiloContador(20);
hUno.start();
hDos = new HiloContador(40);
hDos.start();
}
#SuppressWarnings({ "deprecation", "static-access" })
public void actionPerformed(ActionEvent e) {
if(e.getSource().equals(bUno)){
hUno.parar();
bUno.setLabel("1 parado");
}else if (e.getSource().equals(bDos)){
hDos.parar();
bDos.setLabel("2 parado");
}
}
public void paint(Graphics g) {
while (true){
g.clearRect(1,1,getSize().width,getSize().height); //dibuja la ventana
g.setFont(fuente);
g.drawString(hUno.getContador()+"",40,60);
g.drawString(hDos.getContador()+"",100,60);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
in case it helps anyone, solved deleting the infinite loop and adding this method
Timer timer = new Timer();
timer.schedule( new TimerTask() {
public void run() {
repaint();}
}, 0, 1000);