i have a scheduled task that runs every 5 mins, if everything went ok.
if the last execution of this scheduled task returned false, the delay
should be 10 mins.
how do i do this?

here's a code sample (using 5-minute [fixed-rate] delays):

java.util.Timer myTimer = new java.util.Timer();
myTimer.schedule(new MyRunner(), 0, 300000);

...

static class MyRunner extends TimerTask {
  public void run() {
     FileOpenTask myTask= new FileOpenTask();
     myTask.openFile("myFile.txt");
  }
}

....

public class FileOpenTask {
  // the returned value of this method is, at this point, useless to
the caller
  public boolean openFile(String filename) {
     try {
       FileInputStream fstream = new FileInputStream(filename);
     } catch (FileNotFoundException fnfe) {
        return false;
     }
     return true;
  }
}