waiting threads until it gets value

[focode]

this problem is related to j2me environment , but threads are every
where hence i am asking it here ...

it goes like this ..
application has to check gprs connection on the mobile , this is done
in separate thread , it is implemented thing like this

public void run() {
try{

String url = "http://www.virtuosos.in/sms/gprs/pushsms_gprs_patna.php?
mobileno=000&msg=INNOLABS%20PATNAMOBILE%20DIRECTORYSEARCH%20STDBYCODE
%200612";

text = gnp.processServerResponse(url).trim(); // seperate class to
fetch url data

System.out.println("value returened = "+text);
}catch(Exception e){}

if(text.equals("error"))
{
// url_hit = "no";
switchDisplayable(null, getPacketdatamissing());
}
else
{
url_hit = "yes";
}

}


"run" method is invoked from here

public void check_gpr() {

Thread t = new Thread( this );
t.start();
if (url_hit.equals("no")) {

switchDisplayable(null, getPacketdatamissing());

} else {

switchDisplayable(null, getMainMenu());

}

}

checking gprs data takes some time , in the mean time
"switchDisplayable(null, getMainMenu());" is called , while the
process of checking gprs continues, and when the application founds
that gprs is not subscribed , it takes appropriate action , (and exits
the program ). what is required is .. until and unless the checking
of gprs is verified , the program should not take any further action ,
and should wait their itself , i think use of "wait" function should
solve my problem , can any one guied me where to put "wait" to solve
this problem, i shall be highly thankfull.

thanks and regards
Arunesh

 

[John B. Matthews]

checking gprs data takes some time , in the mean time
"switchDisplayable(null, getMainMenu());" is called , while the
process of checking gprs continues, and when the application founds
that gprs is not subscribed , it takes appropriate action , (and
exits the program ). what is required is .. until and unless the
checking of gprs is verified , the program should not take any
further action , and should wait their itself , i think use of "wait"
function should solve my problem , can any one guied me where to put
"wait" to solve this problem, i shall be highly thankfull.

As suggested recently

<http://groups.google.com/group/comp.lang.java.programmer/browse_frm/thread/f061fbea51b6d333>

consider the cancelable wait approach, shown here:

<http://developers.sun.com/mobility/midp/articles/threading/>

If your application checks gps often, the section on "Using One
Thread for Network Activity" may be especially apropos.

 

[Tom Anderson]

checking gprs data takes some time , in the mean time
"switchDisplayable(null, getMainMenu());" is called , while the process
of checking gprs continues, and when the application founds that gprs is
not subscribed , it takes appropriate action , (and exits the program ).
what is required is .. until and unless the checking of gprs is verified
, the program should not take any further action , and should wait their
itself , i think use of "wait" function should solve my problem , can
any one guied me where to put "wait" to solve this problem, i shall be
highly thankfull.

It's not clear to me what you want. Is it that the application should
first display the main menu, and then if later on the GPRS verification
fails, it should switch to the error message and quit? In that case, you
don't necessarily need a wait - the code above will work, although it
could be even simpler:

public void check_gprs() {
new Thread(this).start();
switchDisplayable(null, getMainMenu());
}

public void run() {
// try to download URL
if (text.equals("error")) switchDisplayable(null, getPacketdatamissing());
}

That's all you need.

If you want the program to display the main menu and then wait until the
verification has finished, then you have a couple of options. The simplest
is actually to use join, not wait - join waits for another thread to
finish:

public void check_gprs() {
Thread t = new Thread(this);
t.start();
switchDisplayable(null, getMainMenu());
t.join();
}

If you want a real wait, it's like this:

private boolean verificationComplete = false;

public void check_gprs() {
new Thread(this).start();
switchDisplayable(null, getMainMenu());
synchronized (this) {
// you need to decide what to do with InterruptedException here
while (!verificationComplete) wait();
}
}

public void run() {
// try to download URL
if (text.equals("error")) switchDisplayable(null, getPacketdatamissing());
synchronized (this) {
verificationComplete = true;
notifyAll();
}
}

tom

--
But in natural sciences whose conclusions are true and necessary and
have nothing to do with human will, one must take care not to place
oneself in the defence of error; for here a thousand Demostheneses and
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who happened to hit upon the truth for himself. -- Galileo