Java multi threading - Passing a data-structure to the thread

Question

The application, I am writing, generates an ArrayList of Characters at certain stage. At this stage, I am trying create a thread to process this ArrayList. The problem is how do I pass this ArrayList to the thread

Descriptive Code:

class thisApp {
    /* Some initial processing creates an ArrayList - aList */

    Runnable proExec = new ProcessList (); //ProcessList implements Runnable
    Thread th = new Thread(proExec);
}

Descriptive Code For ProcessList:

public class ProcessList implements Runnable {
    public void run() {
      /* Access the ArrayList - aList - and do something upon */
    }
}

My problem is: How do I pass and access aList in run()?

NPE · Accepted Answer · 2011-06-10 17:07:10Z

6

You can simply pass aList to the ProcessList's constructor, which can retain the reference until it's needed:

class thisApp {
    /* Some initial processing creates an ArrayList - aList */

    Runnable proExec = new ProcessList (aList);
    Thread th = new Thread(proExec);
}

public class ProcessList implements Runnable {
    private final ArrayList<Character> aList;
    public ProcessList(ArrayList<Character> aList) {
      this.aList = aList;
    }
    public void run() {
      /* use this.aList */
    }
}

N.B. If aList will be accessed concurrently by multiple threads, with one or more threads modifying it, all relevant code will need to be synchronized.

answered Jun 10, 2011 at 17:07

NPE

503k114 gold badges970 silver badges1k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

check123 Over a year ago

It is highly unlikely that the list will be simultaneously accessed. Anyways, Thanks!

Matt Ball · Accepted Answer · 2011-06-10 17:06:36Z

4

Add an argument to the ProcessList constructor.

public class ProcessList implements Runnable
{    
    private final List<Foo> aList;

    public ProcessList(List<Foo> aList)
    {
        this.aList = aList;
    }

    public void run()
    {
      System.out.println(aList.size());
    }
}

You'll have to be careful about concurrent access to the list if any other threads have access to it.

answered Jun 10, 2011 at 17:06

Matt Ball

361k102 gold badges655 silver badges725 bronze badges

Comments

Joel · Accepted Answer · 2011-06-10 17:08:49Z

2

You could make the List final, but it's better to pass it in to your Runnable object.

public class ProcessList implements Runnable {
    List<Character> list;
    public ProcessList(List<Character> list){
    this.list = list;
    }
    public void run() {
         this.list.size();
    }
}

answered Jun 10, 2011 at 17:08

Joel

30.3k36 gold badges113 silver badges140 bronze badges

2 Comments

Matt Ball Over a year ago

"You could make the List final" - I don't get what you're saying there.

Joel Over a year ago

I was suggesting that if the list was in scope then by making it final you could reference it from within the threads run method without passing it in.

Collectives™ on Stack Overflow

Java multi threading - Passing a data-structure to the thread

3 Answers 3

1 Comment

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related