Threads: Retrieving then executing object from ArrayList

Question

I am working with threads and need to first retrieve an object from a collection and then execute the method in that object. I used the ArrayList.get(0) to retrieve the first element, but now how do I execute the run() method for my Runnable object that I just retrieved?

Here is my code so far:

public class MyThread extends Thread{

//Instance Variables
private List<Runnable> requestQueue;

//Constructor
public MyThread() {
    requestQueue = new LinkedList<Runnable>();
}

//Methods
public void run() {
    while (!requestQueue.isEmpty()) { 
        try {
            wait();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        requestQueue.get(0);
    }
}

}

Is there a reason you need to execute each Runnable task in sequences? — Santosh Gokak
– Santosh Gokak, Commented Nov 7, 2012 at 1:11
Might I suggest that something in the java.util.concurrent package such as ExecutorService could provide the functionality you're looking for? — logan
– logan, Commented Nov 7, 2012 at 1:33
instead of using List, you may want to use Queue or BlockingQueue — tanyehzheng
– tanyehzheng, Commented Nov 7, 2012 at 1:34
@logan Yes, I'm told that ExecutorService makes life much easier, however, I'm doing this for a homework assignment and they want us to have a better understanding of threading, wait/notify, and synchronization... — neuquen
– neuquen, Commented Nov 7, 2012 at 1:39

Reimeus · Accepted Answer · 2012-11-07 01:36:08Z

2

While you queue is not empty you can run:

new Thread(requestQueue.get(0)).start();

BTW: You should be getting a cyclic name conflict indicating that you can't extend Thread. You could rename the class to, say, MyThread.

Also have a look at ExecutorService as a means of abstracting many of the complexities associated with the lower-level abstractions like raw Thread.

edited Nov 7, 2012 at 1:36

answered Nov 7, 2012 at 1:14

Reimeus

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5 Comments

neuquen Over a year ago

Well, this isn't my main method, but in my main method I plan on creating the new thread. In which case, the new operator would not be necessary here, right?

neuquen Over a year ago

It's actually called by a different name, but I wanted it to be as general as possible.

Reimeus Over a year ago

Yes, that's fine but would suggest calling your class something other than Thread...

neuquen Over a year ago

If I were to create a new Thread in myThread then what you stated would be correct, but if I intend on creating the new Thread in another class then my code in myThread would need to be requestQueue.get(0).run();

Reimeus Over a year ago

No. just calling run() does not make it a Thread. You need to wrap your Runnable objects in new Threads for them to be threaded.

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