Develop Reference

How do I only delay a specific method?

I am still a very early coder and still don't know everything about java so my code is still a bit messy, sorry about that. I am making a simple platformer game with the graphics g class and I'm trying to figure out how to delay a method without pausing the entire script.
I have tried Thread.sleep() and TimeUnit.SECONDS.sleep() but both of these freeze other methods running at the time, and the Timer that keeps the game running.
private static Timer timer;
private int delay = 10;
public Gameplay() {
addKeyListener(this);
setFocusable(true);
setFocusTraversalKeysEnabled(false);
timer = new Timer(delay, this);
timer.start();
}
public void moveDown() {
if (play == true) {
Playsound("drop");
dropping = true;
//pause here for 1 second without freezing timer or other running methods
dropping = false;
}
}
I want the program to continue running while waiting, but the things I have tried always freeze the entire program

One trick from my side
public void moveDown() {
if (play == true) {
Playsound("drop");
dropping = true;
//create a thread which will execute your method and set sleep on that thread
dropping = false;
}

try this
...
Thread thread = new Thread(() -> moveDown());
thread.run();
...
void moveDown() {
//do some work
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
//continue your work
}
explanation
you need to stop thread , but you dont want to stop current thread :)
that means you need to run your work on background thred and stop only it,
this is not best solution , its just for explanation how you can do it.

Delaying a java programme involving a GUI without Thread.sleep()

I'm currently programming a mini game in java swing. I've got the GUI set up, and the game involves a sequence of numbers flashing up on screen and then disappearing - the user must then input the numbers again in the sequence they appeared.
When the numbers are initially displayed, I want them to display for 1-2 seconds, and then disappear, and have another number for 1-2 seconds etc.
However, I'm having issues with delaying the program whilst the number displays. I can't use Thread.sleep as it pauses the whole program with the hiding of previous numbers etc. It just doesn't work. I've tried every other suggestion I've come across, none of which have worked yet.
Anyone got anymore tips?

int delay = 5000; // delay in milliseconds
ActionListener taskPerformer = new ActionListener() {
public void actionPerformed(ActionEvent evt) { //...Perform a task... } };
Timer timer = new Timer(delay, taskPerformer);
timer.setRepeats(false);
timer.start(); // timer starts - after delay time your task gets executed
Source

You can use Thread.sleep()
The problem you having is probably because you are trying to update the UI from Swing's event dispatching thread. This is a thread that is reserved for Swing components and you should do exactly nothing in it except quick updates to the UI.
public void prog() {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
label.setText("1");
}
}
try {
Thread.sleep(5000);
} catch(Exception e) { }
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
label.setText("2");
}
}
}
public static void main(String[] args) {
label = new JLabel("0");
prog();
}
JLabel label
The UI should remain responsive because of it's component interactions should be implemented in ActionListener's. But if you want to perform other work while waiting, or if the feature is contained in an ActionListener's actionPerfomed() method, you can kick off a new thread to sleep 5 seconds then update the UI. You could also perform some calculations that take 5 seconds to compute instead of sleeping without blocking the UI. The code would be:
(new Thread(new Runnable() {
#Override
public void run() {
try {
Thread.sleep(5000);
} catch (Exception e) { }
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
label.setText("2");
}
}
}
}).start();

Thread.sleep() to swing Timer conversion

I am trying to implement a Thread.sleep(6000) line but it seems to freeze in the applet. When I tried to use Timers, I wasn't sure how to use because I am not very good with event listeners. I am basically trying to call a method fetchUrl() every 6 seconds, after the user clicks the enter button. How can I implement this?
public void init() {
c = getContentPane();
c.setLayout(flow);
c.setBackground(forum);
question.setForeground(Color.white);
question.setFont(tnr);
question2.setForeground(Color.white);
question2.setFont(tnr);
result.setForeground(Color.white);
result.setFont(tnr);
resp.setBorder(BorderFactory.createBevelBorder(0));
timeLength.setBorder(BorderFactory.createBevelBorder(0));
c.add(question);
c.add(resp);
c.add(question2);
c.add(timeLength);
c.add(enter);
c.add(result);
resp.requestFocus();
enter.addActionListener(this);
t = new Timer(DELAY, this);
t.setInitialDelay(DELAY);
}
public void actionPerformed(ActionEvent e) {
final String n1;
int timeMin, timeSec, count = 0, maxCount;
timeMin = Integer.parseInt(timeLength.getText());
timeSec = timeMin * 60;
maxCount = (int)(timeSec/6);
if (e.getSource() == enter) { //user clicks enter
n1 = resp.getText();
while (count < maxCount) {
fetchUrl(n1); //this method called every 6 seconds
t.start();
count++;
}
}
}

First I would start by separating the ActionListener for the Timer and for the JButton.
Second nothing is happening logically with the Timer because you're swallowing it with the button source check.
Third you should understand how the timer works. Basically for every "tick" (in your case six seconds) the actionPerformed of the timer ActionListener is called. So if you want the fetch() method called, then that's what you should be visible/accessible to the in the Timer's actionPerformed.
The button's ActionListener should only handle the starting of the timer I believe. So just separate the listeners. Give each one an anonymous ActionListener and no need to make the class implement ActionListener.
For example
timer = new Timer(DELAY, new ActionListener(){
public void actionPerformed(ActionEvent e) {
// do some stuff every six seconds
fetchURL();
}
});
enter = new JButton(...);
enter.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e) {
timer.start();
}
});
If you want some automatic stopping feature for the timer, you could do something like
timer = new Timer(DELAY, new ActionListener(){
public void actionPerformed(ActionEvent e) {
if (someStoppingCondition()) {
timer.stop();
} else {
// do some stuff every six seconds
fetchURL();
}
// do some stuff every six second
}
});

You need to call a method after user clicks on button every 6 seconds, but you have not said how many times you want to call it.
For infinite number of times, try something like the following,
while(true){
new Thread(){
#Override
public void run(){
try{
Thread.sleep(6000);
fetchUrl(n1);
}catch(InterruptedException e){}
}
}.start();
}
If you will use Thread.sleep() in your applet, then your applet will be hanged for 6 seconds and so create a new thread for it.

How to Interrupt in Java

In Java, let's say I have a GUI with 2 buttons, Go and Pause.
When I press Go, "Hello" gets printed out over and over again. When I press Pause, "Hello" no longer gets printed to the screen.
Example: User presses Go button. "Hello" gets printed out for 1 minute until the user presses "Pause."
What is the proper way to express this approach in Java? Is it equivalent to my commented pseudocode within the goButton source?
public void actionPerformed(ActionEvent e) {
if(e.getSource() == goButton)
{
// while user has not pressed the pause button
printHello();
}
else if(e.getSource() == pauseButton)
{
pause();
}
}
Thanks

In order to get this to work, in reasonable fashion, you will need a Thread. This is executed in the background until such time as you decide to cancel/pause it.
This is an EXTREMELY basic example. Normally I'd wrap the task and the GUI up in appropriate classes rather then accessing static references, but it gives a basic idea
public class TestHello {
private static HelloTask task;
public static void main(String[] args) {
Thread thread = new Thread((task = new HelloTask()));
thread.setDaemon(true);
thread.start();
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new GridBagLayout());
frame.setSize(200, 200);
frame.setLocationRelativeTo(null);
JButton goButton = new JButton("Go");
JButton stopButton = new JButton("Stop");
goButton.setActionCommand("Go");
stopButton.setActionCommand("Stop");
ActionHandler handler = new ActionHandler();
goButton.addActionListener(handler);
stopButton.addActionListener(handler);
frame.add(goButton);
frame.add(stopButton);
frame.setVisible(true);
}
public static class ActionHandler implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals("Go")) {
task.start();
} else if (e.getActionCommand().equals("Stop")) {
task.pause();
}
}
}
public static class HelloTask implements Runnable {
private static final Object WAIT_LOCK = new Object();
private boolean dump = false;
public void start() {
synchronized (WAIT_LOCK) {
dump = true;
WAIT_LOCK.notify();
}
}
public void pause() {
synchronized (WAIT_LOCK) {
dump = false;
WAIT_LOCK.notify();
}
}
#Override
public void run() {
while (true) {
while (dump) {
System.out.println("Hello");
}
try {
synchronized (WAIT_LOCK) {
WAIT_LOCK.wait();
}
} catch (Exception e) {
}
}
}
}
}
Some further read:
Java Concurrency
Concurrency in Swing
Caveats
NEVER try and modify the GUI from any thread other then the Event Dispatching Thread.

To have responsive UI you would usually have to run printHello() in separate thread. Then as you do processing in this thread, for example, after every print statement, you check some flag boolean isPaused; and stop execution if it is true. When pause button is clicked you set the value of this flag to true.

You need to implement your loop in a separate thread. Otherwise the GUI will become irresponsive and the user might not be able to click the Pause button at all.
With this threaded approach, you also need a flag which indicates whether or not to print out the message. The printing loop can simply stop executing the thread when the flag is set to no longer print.

what about htis:
boolean flag=true;
public void actionPerformed(ActionEvent e) {
if(e.getSource() == goButton)
{
while(true)
{
printHello();
}
}
else if(e.getSource() == pauseButton)
{
pause();
}
}

You can do this in a few ways the simplest being:
You have a boolean flag, keepPrinting and you set it to true when you push the Go button, false when you push the Pause. Next you have a thread somewhere executing a while loop which will print nothing when keepPrinting is false.
The threading here is really important, without it you're going to have your GUI freeze once the user pushes a button as the program prints hello and happily ignores anything else.
Pseudo Code
//GUI
public ThreadedPrinter greeter;
void ButtonGoPushed(args){
greeter.keepPrinting = true;
}
void ButtonPausePushed(args){
greeter.keepPrinting = false;
}
//ThreadedPrinter
boolean keepPrinting
void run(){
while(true){
if(keepPrinting){
print("Hello");
}
sleep(5); //Make sure that this thread yields if the system doesn't do it automatically
}
The good news about java concurrency versus say C++ is that this will just work, you don't have to worry about the boolean being crazy and inconsistent because in java variable sets are atomic. If you want to do more than just set the variable, make a synchronized method that sets the variable and does anything else you want.

Basically to keep UI responsive such task need to be performed in other thread.
There can be various ways in which you can implement this mechanism in java.
I have used simple mechanism of Runnalbe and volatile flag which ensure that thread exists when you call cancelPrint() method
public void actionPerformed(ActionEvent e) {
if(e.getSource() == goButton)
{
//start the thread here
}
else if(e.getSource() == pauseButton)
{
//call cancel here
}
}
public class HelloPrinter implements Runnable {
volatile boolean cancel = false;
#Override
public void run() {
while (!cancel) {
printHello();
}
}
public void cancelPrint() {
cancel = true;
}
}

I assume you want to do more than just printouts. Take a look at Swing Worker.
It allows you to pretty easily write your GUI-related code that gets executed in the AWT Event Thread and your long-executing code in other thread(s) and pass values back and forth. This will help prevent any GUI lockup issues you might experience.

How do I make this java for loop pause for 1/2 a second between each iteration?

private class MultipleGensListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
for(int i = 0; i < 25; i++)
{
game.runSimulationOneGen();
changeGrid();
}
}
}
//this is the loop. The changeGrid method displays a game grid on a GUI but
// only the 25th iteration is visible on screen. I would like each one to be
// visible for about a half a second before the loop continues.
// I have seen some questions answered on here that are very close to what I'm asking,
// but I just don't really understand how to apply it to my program..
// thanks for any help.

If the code performed by the simulation is quick and does not consume too much CPU and time, then consider using a Swing Timer to do your looping and delay. Otherwise, you'll need to use a background thread such as can be done with a SwingWorker object.
For e.g. if using both Swing Timer and SwingWorker:
private class MultipleGensListener implements ActionListener {
protected static final int MAX_INDEX = 25;
public void actionPerformed(ActionEvent e) {
int timerDelay = 500; // ms delay
new Timer(timerDelay, new ActionListener() {
int index = 0;
public void actionPerformed(ActionEvent e) {
if (index < MAX_INDEX) { // loop only MAX_INDEX times
index++;
// create the SwingWorker and execute it
new SwingWorker<Void, Void>() {
#Override
protected Void doInBackground() throws Exception {
game.runSimulationOneGen(); // this is done in background thread.
return null;
}
#Override
protected void done() {
changeGrid(); // this is called on EDT after background thread done.
}
}.execute(); // execute the SwingWorker
} else {
((Timer) e.getSource()).stop(); // stop the timer
}
}
}).start(); // start the Swing timer
}
}

NEVER BLOCK THE GUI EVENT THREAD
you can use a timer for that and have it only fire 25 times
final Timer t = new Timer(500,null);
t.addActionListener(new ActionListener(){
int i=0;
public void actionPerformed(ActionEvent e){
game.runSimulationOneGen();//run 1 iteration per tick
changeGrid();
if(i>25){t.stop();}
i++;
}
});
t.setRepeats(true);
t.start();
btw the reason only the last iteration is shown is that gui updates (redraws) are done in a separate event, but to let another event trigger you need to return from the listener method which you didn't
the Timer I showed is a more elaborate iteration which lets other events run in between iterations allowing the gui to show the changes

check my post that shows both methods java.swing.Timer#setDelay(int)
and
correct usage of Thread.sleep(int)
java wait cursor display problem