Implementing multiple threads in Java

Question

I am pretty new to Java and the project I have requires a new thread to be created every time the user presses a button. I've worked with the MVC and Swing but I am trying to find a way to create however many threads the user needs. I reviewed some information and was trying to use an arrayList to just collect all the threads. However I am having some problems with this:

private ThreadLibrary thread_lib = new ThreadLibrary(); 

    public TestArray(int val) {
        for (int i=0; i < val; i++) {           
            thread_lib.addThread(    new Thread(new runThread()).start()   );       
        }
    }

Since the new operator doesn't return anything it won't add anything to the arrayList. Any ideas or a better data structure to use? Thanks

Samir Talwar · Accepted Answer · 2011-04-30 01:24:45Z

1

new definitely returns whatever you're constructing. It's the start method which returns void. Try storing the thread object in a variable and kicking it off separately.

public TestArray(int val) {
    for (int i = 0; i < val; i++) {       
        Thread thread = new Thread(new runThread());
        thread.start();
        thread_lib.addThread(thread);       
    }
}

answered Apr 30, 2011 at 1:24

Samir Talwar

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1 Comment

othnin Over a year ago

Thanks for the help and the clarification on what is returning void.

sbridges · Accepted Answer · 2011-04-30 01:23:49Z

1

This,

thread_lib.addThread(    new Thread(new runThread()).start()   )

should be,

Thread t =  new Thread(new runThread());
thread_lib.addThread(t);
t.start();

Instead of doing this, look at the ThreadPoolExecutor class

answered Apr 30, 2011 at 1:23

sbridges

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2 Comments

othnin Over a year ago

one more question. Is there an easy way to pass any paramters to the runThread class? If I put it in new runthread() it shouldn't really be usable since t.start will kick off the run() method.

othnin Over a year ago

Ok - it seems to work but I guess don't really understand why. I assume it runs the constructor before it becomes a thread and goes to run(). Not sure if that will work for me in the long run.

Ernest Friedman-Hill · Accepted Answer · 2011-04-30 01:24:50Z

0

new does indeed return the Thread; it's the call to start() that returns void. You can simply do this in two steps:

Thread t = new Thread(new runThread());
t.start();
thread_lib.addThread(t);

Now, whether you actually need to put these in an array or not is open to question; there isn't too much you can do to a Thread after it's running.

answered Apr 30, 2011 at 1:24

Ernest Friedman-Hill

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