Question

I have a simple applet on a web page like this. (This is a test case cut down from a more complicated applet).

package test;

import java.applet.Applet;

@SuppressWarnings("serial")
public class SimpleLoopApplet extends Applet
{
    public void init()
    {
        System.out.println("SimpleLoopApplet invoked");
        try
        {
            while (true)
            {
                try
                {
                    System.out.println("Sleep for 1 second");
                    Thread.sleep(1000);
                }
                catch (InterruptedException e)
                {
                    System.out.println("Applet thread interrupted while sleeping");
                }
            }
        }
        finally {}
    }
}

On Firefox 3.6.8 on one computer this applet will run for 20 seconds and then exit abruptly, as if the VM is terminating (The java console will disappear; the Java icon will remain in the system tray until I mouse over it; the finally block is never reached).

It’s consistently 20 seconds. 20 “Sleep for 1 second”s printed from the above code, if I extend the sleep to 5 seconds, then 4 messages are printed before termination.

In IE and Chrome on the same computer, the loop will continue on indefinitely, as it will in Firefox 3.6.8 on a different computer.

Can anyone suggest why the applet might terminate in this way?

Answer 1

From the applet tutorial

init Method

The init method is useful for one-time
initialization that doesn’t take very
long. The init method typically
contains the code that you would
normally put into a constructor. The
reason applets don’t usually have
constructors is that they aren’t
guaranteed to have a full environment
until their init method is called.
Keep the init method short so that
your applet can load quickly.

start Method

Every applet that performs tasks after
initialization (except in direct
response to user actions) must
override the start method. The start
method starts the execution of the
applet. It is good practice to return
quickly from the start method. If you
need to perform computationally
intensive operations it might be
better to start a new thread for this
purpose.

It looks like you have to create your own thread for long running methods.