Java – Making a J2ME Midlet sleep without threads

javajava-memidletmidpscheduling

Quick question … Using J2ME (CLDC 1.1, MIDP-2.1) is it possible to sleep the Midlet for a period of time (not using threads)… For example:

public class myMidlet extends MIDlet{
    public void startApp() {
        /* Sleep for 10 seconds */

        /* The answer was: */
        try {
            Thread.sleep(time_ms);
        } catch (Exception e) {}
    }
...

I don't use Java all that much, and don't want to program threads just for a simple sleep.

Thanks in advance

Answer Summary

My lack of Java knowledge. Examples I saw using Thread.sleep() led me to believe it was only usable in a thread object spawned by the Midlet … not the midlet itself. I didn't want to have to spool off the midlet logic into a thread to sleep it … But now I know the midlet runs in the default thread 🙂 Going to find that Java book I never read because I didn't think I would use the language ever

Best Answer

I didn't understand whether you mean putting midlet in paused state or just stopping execution for specified time.

If it's the latter, actually I don't undesrtand, why you don't want to use Threads, this is no big deal. You just insert three following lines wherever you need:

try {
    Thread.sleep(10000);
} catch (Exception ex) {}

That's all, nothing too complicating.

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There's lots of Java code coverage tools. Many of them work by using JVM features not available in embedded systems due to space limitations.

One that uses only an additional boolean array in which to hold the coverage data can be found at

http://www.semanticdesigns.com/Products/TestCoverage/JavaTestCoverage.html

You have to code an additional routine that dumps that array out of your embedded device into a file on a PC, but that's generally a pretty easy task (e.g., several hours work, once).

Java – Difference between wait() and sleep()

A wait can be "woken up" by another thread calling notify on the monitor which is being waited on whereas a sleep cannot. Also a wait (and notify) must happen in a block synchronized on the monitor object whereas sleep does not:

Object mon = ...;
synchronized (mon) {
    mon.wait();
}

At this point the currently executing thread waits and releases the monitor. Another thread may do

synchronized (mon) { mon.notify(); }

(on the same mon object) and the first thread (assuming it is the only thread waiting on the monitor) will wake up.

You can also call notifyAll if more than one thread is waiting on the monitor – this will wake all of them up. However, only one of the threads will be able to grab the monitor (remember that the wait is in a synchronized block) and carry on – the others will then be blocked until they can acquire the monitor's lock.

Another point is that you call wait on Object itself (i.e. you wait on an object's monitor) whereas you call sleep on Thread.

Yet another point is that you can get spurious wakeups from wait (i.e. the thread which is waiting resumes for no apparent reason). You should always wait whilst spinning on some condition as follows:

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