Question

I have a driver class called Advantech which is stored inside an ArrayList. I instantiate and initialize my class. The Advantech class extends Thread and the Advantech class has a run() method. The thread is started within the class once it makes the connection to the device. (this.start();)

Is it possible to start the thread then store the instance of that class into an ArrayList?

When I instantiate the class and store it back into the array list (overwriting the previous position) with set(pos, class), I get NullPointerException when I call class.isAlive().

Are there any alternatives/better ways to do this?

I know this may sound strange, but I am using ArrayList because otherwise I have to create eight classes to start eight threads, for example:

Advantech adv1;
Advantech adv2;
Advantech adv3;
Advantech adv4;

All the parameters are the same for each instance.

Code:

private ArrayList<Advantech> advantech = null;
private Advantech adv = null;
....

adv = new Advantech(/* parameters */);

adv.initialize();

advantech.set(0, adv);

In Advantech.java:

public class Advantech extends Thread {

    ....
    public void run() {

         while(!done) { // do some work }
    }
}

Answer 1

Unless I’ve missed something (or you just haven’t posted it), you don’t seem to have constructed your ArrayList<Advantech> anywhere. You need this line before using it:

// Here, numOfThreads is an int variable that specifies how many threads you want to store
advantech = new ArrayList<Advantech>(numOfThreads);

Also, you might want to rename the list to something more descriptive (maybe advantechThreadList.)