Adding gravity into a Java applet

Hey guys,
I have an array of 10,000 dots (ovals) on my screen, and I am trying to make a simple physics simulator, that simulates gravity between these dots. I would like them to interact.
I'm not really sure where to start, Im not sure if there is a Java method that does this, but anyhow, can someone please explain to me how i would go about doing somthing like this.
Thanks in advance!
Andrew

sabre150 wrote:
masijade. wrote:
Futurisdom_Developer wrote:
Have a thread in an infinite loop that loops through each dot.
Everytime it checks a dot, it adds x amount of speed to the object (obviously down, seeing as gravity is pulling it down).
Hope this helps.Except that he wants gravity between the dots (i.e. as in between the Sun and the Earth).and 10,000 masses require each of the 10,000 to compute the interaction with the other 9,999 so there are about 100,000,000 calculations per iteration.I guess I should have further refined the quote, as I was taking note of "down" part. ;-)
Edit: And the "down" makes it sound as though he is talking only about adding in one direction, rather than adding in the direction from which the next dot is coming, and simply adding one does not, of course, take proximity, or mass into account, which it would need to.

Similar Messages

Adding a KeyListener to java applet

I'm going to post this again, because I didn't really understand the last answer.. I know how to add KeyListeners to textfields and buttons, etc, but how do I add it to the applet itself.. I want to do this because I have a painted box on the screen and I want it to move its position everytime I hit the up key.. But I can't add the keylistener to anything but textfields and stuff. I dont know how to do it. Can u please help.. Someone told me JApplet.addKeyListener(this); but I tried it and it didn't work.. It gave me an error cannot find symbol JApplet, I dont have a variable for my whole applet, and I'm not sure how to create one either. Can anyone help?

I'm going to post this again, because I didn't really
understand the last answer.. That's no excuse for cross posting.
http://forum.java.sun.com/thread.jspa?threadID=5215206

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Passing Variables From PHP to Java Applet ?

I took one page of a project which was written entirely in PHP, and translated it into a JAVA applet, so as to support better GUI funcitonalities (immediate calculation and display of Time/Billing data, on LostFocus events...stuff like this).
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Updated some code... in case people wanted to use it....
<?php
class JavaApplet {
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$applet = &New JavaApplet;
$applet->setParam("name1", "value");
$applet->setParam("name2", "value");
$applet->setParam("name3", "value");
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Java applets in a browser, and Serial port input

I know that there is a special package for serial port input in java. (java.Comm.SerialPort)
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I have found lots of reference to Serial port input, but nothing that really goes in the direction that I am lookind for.
Any little tid bits of information pertaining to this would be greatly appreciated.
Cuervo

You should also consider that applets are not allowed to access their client system's hardware without being signed; in other words, the user must agree (by clicking a button) to disable the applet security features. Why would you use an applet to do this? Applets are meant to be an extension of a website. You should use an application in this situation.

Copy and Paste into Java Applet

I know there have been some posts like this in the paste, but could not find a reasonable explanation.
JVM 1.4.2_08
For an unsigned java applet (Swing) I could not copy from a notepad document into my applets JTextField and JTextArea fields.
JVM 1.5
For this same applet (Swing) running under 1.5, I could copy and paste from the notepad document into my applets JTextField and JTextArea fields.
Does anybody know why the difference?
Is there a way to copy and paste for applets running in the 1.4.2 jvm?
Thanks.

I think it must be some security restriction.
Set a policy for the applet or sign it:
Set a policy (windows):
C:\Program Files\Java\j2re****\lib\security\java.policy
under grant {
permission java.security.AllPermission;
this means that you give all permission to all code, if you only want to give permissions for applets
comming from google you can add the following:
grant codeBase "http://google.com/-" {
permission java.security.AllPermission;
to sign
http://forum.java.sun.com/thread.jsp?forum=63&thread=524815
second post

Preventing "Paste" into java applets

First of all, I am sorry that I was not able to search these forums. I searched but the "Sun Search" did not seem to allow a specific forum search and threw more than a page of non-forum hits.
I would like to know whether it is possible to prevent paste (as in copy and paste) into the text field of a java applet as run on a browser as part of an online application.
I know that there are javascript applications for preventing "right click" the use of the control keys and also (the best or most annoying in my experience) flushing the system clipboard.
However, all these measures can be circumvented and I thin that the Opera browser in is good at circumventing them.
When it comes to a java applet however, without interferting with the system, I would have thought it would be possible to control
1) Connections to the system clipboard
2) Which keys can be used to enter into a text field.
So I would have though that preventing paste into a java text field would be possible.
But today I was asked "Do you understand computers"? And made a fool of when I suggested that such a thing may be possible, by a Java programmer. I am surprised.
Is it possible to prevent paste (ctrl v, or using the mouse) into a java text field?
Tim

cleaner way to do it (cleaner meaning not so many inner classes!) is to just add a key adapter to whatever text component you want (textfields, textareas, anything that takes KeyListener)
example..
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import java.awt.*;
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}by calling addKeyListener(new NoPaste()); with each component you want, you can disable the ctrl+v key function. the negative side is that a context menu (or any other 3rd party component) could still call paste(), but then again they could call setText anyway, so its not much difference. not to mention Swing does not feature context menus by default..

How to add images into a java application (not applet)

Hello,
I am new in java programming. I would like to know how to add images into a java application (not an applet). If i could get an standard example about how to add a image to a java application, I would apreciated it. Any help will be greatly apreciated.
Thank you,
Oscar

Your' better off looking in the java 2d forum.
package images;
import java.awt.*;
import java.awt.image.*;
import java.io.FileInputStream;
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Turning a Java applett into a *.exe

How do you turn a Java applett into an *.exe?

Have a look at http://gcc.gnu.org/java/. Its not complete, and I've never tried it on Windows, but it kinda works for linux.
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Php adding java applet

Hi, I new to java and php and I want to use php and using java applet. How to add java applet into php. Please Help me.

How to add java applet into php. Please Help me. If it is working in html why don't you puts those tags in your php page.
something like this. But i don't know your PHP server support java..
<?php
Your php here
?>
<applet code="MyApplet.class" width=100 height=140></applet>
<?php
more php here
?>Edited by: sunish_jose on Jan 29, 2009 12:41 PM

Adding an image in a java applet

Hey everyone... I am using Jbuilder and trying to add an image or background image in my applet. The image is in the folder the java file runs out of. I would really appreciate it if anyone could help me..

I use this to add an image that I have saved in the applet folder
Image image;
public void init() {
image = getImage(getDocumentBase(), "auburn.jpg");
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java.lang.NullPointerException
     at java.applet.Applet.getDocumentBase(Applet.java:125)
     at JavaProject.<init>(JavaProject.java:103)
     at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
     at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
     at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
     at java.lang.reflect.Constructor.newInstance(Constructor.java:274)
     at java.lang.Class.newInstance0(Class.java:308)
     at java.lang.Class.newInstance(Class.java:261)
     at sun.applet.AppletPanel.createApplet(AppletPanel.java:617)
     at sun.applet.AppletPanel.runLoader(AppletPanel.java:546)
     at sun.applet.AppletPanel.run(AppletPanel.java:298)
     at java.lang.Thread.run(Thread.java:534)
What could be the problem?

Adding a java applet in Apex page

Hello, I am trying to add a java applet to my page. This is what I do. I create an html region with source ;
<applet width=300 height=300 codebase="#WORKSPACE_IMAGES#DrawingLines.class"></applet>
and I upload DrawingLines.class file as a static file.
When I run the page I see the java cup sign (with running circle around) but not the applet. Does this have to do anything with the browser security? My knowledge of Java is very limited, but I thought this should work.
George

I just feel like I have to answer this and I hope this is the last post in this thread.
"I find it amusing that you have come to this forum demanding free technical support, and have posted over 200 times, but you yourself have never once answered somebody's question and gotten a helpful or correct reward"
First of all, I have helped people on a few occasions , I don't know what kind of "helpful or correct reward" you are referring to but yes I have given useful answers and gotten "thank you" from a few members.
Second, most of my posts are from year or more ago when I was learning Apex, I have very few posts in the last 6-12 months.
Third, if nobody asks the questions then there will be no answers => there will be no forum. The very existence of this forum is based on people asking question so why should I be ashamed to "demand free technical hellp", isn't this what most people are doing here?
The rest of your post is just words pretty much not saying anything (you might wanna try a carier in the politics) so I am not going to address it.
Have a wonderful day.

Some Java applets do not work after silent installation, solved by toggling "Enable Java content in the browser" - Why?

We have about 1,800 workstations running Windows 7 (both 32-bit and 64-bit) running various versions of the Java JRE from 6 update 32 through 7 update 51. Most are on 6 update 45. We would like to standardize on Java 7 update 51 (32-bit) and get everyone updated to that version for security reasons.
For the past two weeks, we have been having trouble with our installation pre-pilot. What we are seeing is that our procedure successfully closes any open Internet Explorer windows and Java-related processes, uninstalls all old versions of the Java JRE, and then claims to have successfully installed Java 7 update 51. The Java Control panel works. We can even take Internet Explorer to Verify Java Version or Java Tester - What Version of Java Are You Running? and confirm that the Java applets on those sites are loading (though the latter only works after adding the site to the exceptions site list); however, when testers try to access our Kronos Workforce Central 6.3.10 system, the Java applets used by that system do not load.
We have tried the following things, none of which worked:
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Clear the local Java cache.
Reboot the computer.
Reset Internet Explorer settings, including personal settings.
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javaclean.ps1:
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install.vbs
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'* Date:   3/14/14
'* Author: [REDACTED]
'* Rev:    1.0
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Help on this issue would be much appreciated!

It turns out that this is actually a problem with Kronos Workforce Central. We had the "site.java.plugin.CLSID.familyVersion" setting in that application set to "clsid:CAFEEFAC-0016-0000-FFFF-ABCDEFFEDCBA", which is the Java CLSID for Java 6. After updating this value to "clsid:8AD9C840-044E-11D1-B3E9-00805F499D93" (the Java universal CLSID), this problem did not occur upon the automatic upgrade of Java.
We have both Java 6 and Java 7 in our environment, and did during our Kronos implementation, so I don't know why we were using the Java 6 CLSID in the first place.
Case closed!

Java Applet IIOP Call-In with Release 3C--How do we speed updownload ti

We have successfully implemented a simple Java Applet that calls into
Forte Services via IIOP. However, the duration of the download time for
Applet and its required class files is UNACCEPTABLE in a typical
INTERNET environment where 28.8K modems and multiple hops around the net
are not uncommon. We dialed into our network at 28.8K (but no hopping),
and found that download times varied from 1.5 - 2.0 minutes. This is
unacceptable, even by internet standards. We have been using the
Visigenic Visibroker product as the ORB.
After doing some investigation, we've come up with several ideas to
speed up download time:
1. Figure out how to use the Visigenic components (CORBA/IIOP class
files) that come bundled with the latest version of the Netscape
Navigator browser, so that they don't have to be downloaded
2. Figure out how to use ZIP files. Here's what I've read: "Since the
introduction of Netscape Navigator 3.0, you can specify an uncompressed
.zip file as an addition to the code base of your application. By
specifying a ZIP file, the browser will load your applet's classes from
a specified ZIP file before it searches the code base. This ZIP can
improve applet download time by reducing the number of HTTP connections
required to fetch applet code. As an added benefit, Netscape caches the
single ZIP file so that it will not reload your applet unless the date
of the ZIP file has changed."
3. Figure out how to use JAR files. Here's what I've read: "JAR
stands for Java archive. It's a file format based on the popular ZIP
file format and is used for aggregating many files into one. Although
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can be downloaded to a browser in a single HTTP transaction, rather than
opening a new connection for each piece. This greatly improves the
speed with which an applet can be loaded onto a web page and begin
functioning. The JAR format also supports compression, which reduces the
size of the file and improves download time still further."
Unfortunately, we've been unable to get any of these approaches to work.
Has any one used these or other approaches to speed up applet download
time? Or, does anyone know of consulting firms that specialize in this
sort of thing?
Thanks in advance for your help.
Mike Nelson, Project Leader
Metrix, Inc.
[email protected]
414-798-8560 x1157

We have successfully implemented a simple Java Applet that calls into
Forte Services via IIOP. However, the duration of the download time for
Applet and its required class files is UNACCEPTABLE in a typical
INTERNET environment where 28.8K modems and multiple hops around the net
are not uncommon. We dialed into our network at 28.8K (but no hopping),
and found that download times varied from 1.5 - 2.0 minutes. This is
unacceptable, even by internet standards. We have been using the
Visigenic Visibroker product as the ORB.
After doing some investigation, we've come up with several ideas to
speed up download time:
1. Figure out how to use the Visigenic components (CORBA/IIOP class
files) that come bundled with the latest version of the Netscape
Navigator browser, so that they don't have to be downloaded
2. Figure out how to use ZIP files. Here's what I've read: "Since the
introduction of Netscape Navigator 3.0, you can specify an uncompressed
.zip file as an addition to the code base of your application. By
specifying a ZIP file, the browser will load your applet's classes from
a specified ZIP file before it searches the code base. This ZIP can
improve applet download time by reducing the number of HTTP connections
required to fetch applet code. As an added benefit, Netscape caches the
single ZIP file so that it will not reload your applet unless the date
of the ZIP file has changed."
3. Figure out how to use JAR files. Here's what I've read: "JAR
stands for Java archive. It's a file format based on the popular ZIP
file format and is used for aggregating many files into one. Although
JAR can be used as a general archiving tool, the primary motivation for
its development was so that Java applets and their requisite components
can be downloaded to a browser in a single HTTP transaction, rather than
opening a new connection for each piece. This greatly improves the
speed with which an applet can be loaded onto a web page and begin
functioning. The JAR format also supports compression, which reduces the
size of the file and improves download time still further."
Unfortunately, we've been unable to get any of these approaches to work.
Has any one used these or other approaches to speed up applet download
time? Or, does anyone know of consulting firms that specialize in this
sort of thing?
Thanks in advance for your help.
Mike Nelson, Project Leader
Metrix, Inc.
[email protected]
414-798-8560 x1157

Java Applet Won't Initialize

This is a modified version of a tutorial I've been working with. Code for Main.java:
import javax.swing.*;
public class Main {
* @param args the command line arguments
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JFrame f = new JFrame("Swing Paint Demo");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(300,300);
f.setVisible(true);
Problem is that when I try to load the applet into an html file:
<html>
<APPLET code="Main.class"></APPLET>
</html>
It doesn't load.
The file compiles and executes as a stand alone .jar, but when I try to run it as an applet it won't work.
I know I'm probably missing an easy step. I have already checked my IE7 settings and java is enabled. I have no problem with any other java applets, just the ones I make. haha. Thank you ahead of time.

I did some research, and got a new tutorial because the old one was inappropriate like you pointed out previously. This one I copy pasted into my editor, it compiled fine. I run it through my browser and it doesn't work still. Same issue, coincidentally, what do you make of it?import javax.swing.JApplet;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
//Since we're adding a Swing component, we now need to
//extend JApplet. We need to be careful to access
//components only on the event-dispatching thread.
public class Main extends JApplet {
    JTextField field;
    public void init() {
        //Execute a job on the event-dispatching thread:
        //creating this applet's GUI.
        try {
            SwingUtilities.invokeAndWait(new Runnable() {
                public void run() {
                    createGUI();
        } catch (Exception e) {
            System.err.println("createGUI didn't successfully complete");
        addItem(false, "initializing... ");
    private void createGUI() {
        //Create the text field and make it uneditable.
        field = new JTextField();
        field.setEditable(false);
        //Set the layout manager so that the text field will be
        //as wide as possible.
        setLayout(new java.awt.GridLayout(1,0));
        //Add the text field to the applet.
        add(field);
    public void start() {
        addItem(false, "starting... ");
    public void stop() {
        addItem(false, "stopping... ");
    public void destroy() {
        addItem(false, "preparing for unloading...");
        cleanUp();
    private void cleanUp() {
        //Execute a job on the event-dispatching thread:
        //taking the text field out of this applet.
        try {
            SwingUtilities.invokeAndWait(new Runnable() {
                public void run() {
                    remove(field);
        } catch (Exception e) {
            System.err.println("cleanUp didn't successfully complete");
        field = null;
    private void addItem(boolean alreadyInEDT, String newWord) {
        if (alreadyInEDT) {
            addItem(newWord);
        } else {
            final String word = newWord;
            //Execute a job on the event-dispatching thread:
            //invoking addItem(newWord).
            try {
                SwingUtilities.invokeAndWait(new Runnable() {
                    public void run() {
                        addItem(word);
            } catch (Exception e) {
                System.err.println("addItem didn't successfully complete");
    //Invoke this method ONLY from the event-dispatching thread.
    private void addItem(String newWord) {
        String t = field.getText();
        System.out.println(newWord);
        field.setText(t + newWord);
}

Adding gravity into a Java applet

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