Question

This has been solved by Robin. Thanks Robin!

The idea behind what I want to do is make a timer that performs an action every X seconds, but X has to change between uses.

Right now I’m doing it like this:

 try {
        final FileWriter fstream = new FileWriter("timetest.log");
        final BufferedWriter out = new BufferedWriter(fstream);

        ActionListener task_performer = new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                critical_requests[0]++;
                try {
                    System.out.println("DEBUG: Critical Section requests: " + critical_requests[0] + "\n");
                    out.write("Critical Section request:\t" + critical_requests[0] + "\n");
                } catch (IOException e) {
                    System.out.println(e.getMessage() + "\n");
                }
                ((Timer)evt.getSource()).setDelay( 150 + (rand.nextInt(10) * time_unit ));
            }
        };
        new Timer(wait_delay, task_performer).start();
        System.out.println("Entering while loop\n");
        while(true) {
            if(critical_requests[0] >= 60){
                try {
                    out.close();
                } catch (IOException e) {
                    System.out.println("Close failed for some reason:\t" + e.getMessage() + "\n");
                    System.exit(-1);
                }
                System.exit(0);
            }
            //System.out.println("" + critical_requests[0] + "\n");    // Debug
            critical_requests[0] = critical_requests[0];    // Java is an insane language and it requires me to have this line here
        }
    } catch (IOException e) {
                System.out.println(e.getMessage());
                System.exit(-1);
    }

The error I get is:

local variable is accessed from within inner class; needs to be declared final

I tried making some of them final, but then I can’t change the values inside of the listener. Plus some of the variables don’t make sense to make final (the BufferedWriter out, rand).

All 5 compiler errors are:
local variable rand is accessed from within inner class; needs to be declared final
one each for out, rand, and wait_delay, and two for critical_requests.

How can I reconcile this?

Answer 1

Looking at your code the problem is the wait_delay and the critical_requests variable.

1. There is no real need to change it inside the ActionListener. You will have to set it on the Timer again before it has any effect on the delay of the Timer
2. Creating a new Timer object each time you change the wait_delay variable will result in a lot of Timer instances, which each keep running as a Timer repeats by default. Only if you have called setRepeats( false ) they will actually stop. Looking at your comment (which should have been part of the question), you want to update the delay of the Timer
3. If you really have to change the critical_requests variable inside the ActionListener, you can store it in a final array

So I would suggest to change your code to something like

final int[] critical_requests = new int[]{ 0 };
final Outputstream out = ...;
ActionListener task_performer = new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            critical_requests[0] = critical_requests[0] + 1;
            try {
                out.write("Critical Section request:\t" + (critical_requests[0]) + "\n");
                ((Timer)evt.getSource()).setDelay( 10 + (rand.nextInt() % 10) );
            } catch (IOException e) {
                System.out.println(e.getMessage());
                System.exit(-1);
            }
        }
};
Timer the_one_and_only_timer = new Timer( wait_delay, task_performer );