Why won't get(Calendar.MINUTE) work?????

Question

I am a beginner programmer and am writing some code for my theater company to help our operations in the lighting booth. I want it to pop up a message box at a certain time, say 7:55 pm, that will tell the stage manager to give the actors their 10 minute call. I have tried the following:
int a = calendar.get(Calendar.HOUR_OF_DAY);
int b = calendar.get(Calendar.MINUTE);
while(a==19 && b!=55)
int i = 0;
for(i=0; i<6; i++)
b = calendar.get(Calendar.MINUTE);
JOptionPane.showMessageDialog(null, "Call 10 minutes.");
I have also tried many other things, such as just putting while(calendar.get(Calendar.HOUR_OF_DAY)==19 && calendar.get(Calendar.MINUTE)<55);. Nothing has worked. What appears to me to be happening is that the method get(Calendar.MINUTE) is not updating itself as time changes after the initial run of the statement (I derived this from de-bugging and watching the values change.) Is there any reason for this? Does it just not recognize the finite time change from one minute to the next in the middle of running? Are there any solutions? Thank you!
Addendum: There are no errors in the IDE (Netbeans)
Edited by: cubswar on Mar 25, 2008 5:18 PM

Answer 1

cubswar wrote:
What appears to me to be happening is that the method get(Calendar.MINUTE) is not updating itself as time changes after the initial run of the statement That's correct. A Calendar object doesn't magically update itself as time passes. It's just a representation of an instant in time and certain culture-imposed divsions and labels for that instant.
If you want a Calendar that reflects the time 5 minutes later, then 5 minutes later, you have to create a new Calendar. (Or explicitly set an existing Calendar to that time.)
Also, why would you think this:
for(i=0; i<6; i++)would take a minute or more? It probably takes a few microseconds at most, and quite probably only a fraction of that.
If you want something to happen at a certain time, use Timer and TimerTask, or just do a Thread.sleep for the requisite time. (The easiest is probaly [http://java.sun.com/javase/6/docs/api/java/util/Timer.html#schedule(java.util.TimerTask, java.util.Date)].)