How to access a thread defined in another class?

I have encountered a problem when I want to do a time counting. Basicly the problem is like this: there is a class A, which initiates a private thread in itself, and I have a instant of A in my class B, and in the main method of B I invoked some methods of A and want to test the time to run these methods.

A a = new A();
//start time counter
for (int i = 0; i < 10; i++){ invoke a.method() that takes some time}
//end time counter and prints the time elapsed

but by doing so the method in the for loop will running in a seperate thread in A and the prints method in the last line would probably be executed befo开发者_运维百科re the loop ends. So I want to access the thead in a and invokes a join() to wait until all stuff in the for loop get finished. Could you help me figure how to achieve this? Any ideas would be greatly appreciated.

List All Threads and their Groups

public class Main
{
    public static void visit(final ThreadGroup group, final int level)
    {
        final Thread[] threads = new Thread[group.activeCount() * 2];
        final int numThreads = group.enumerate(threads, false);

        for (int i = 0; i < numThreads; i++)
        {
            Thread thread = threads[i];
            System.out.format("%s:%s\n", group.getName(), thread.getName());
        }

        final ThreadGroup[] groups = new ThreadGroup[group.activeGroupCount() * 2];
        final int numGroups = group.enumerate(groups, false);

        for (int i = 0; i < numGroups; i++)
        {
            visit(groups[i], level + 1);
        }
    }

    public static void main(final String[] args)
    {
        ThreadGroup root = Thread.currentThread().getThreadGroup().getParent();
        while (root.getParent() != null)
        {
            root = root.getParent();
        }

        visit(root, 0);
    }
}

Based on your edits, you might can find out what group and name the thread is and get a reference to it that way and do what you need to do.

For your own code in the future

You want to look at ExecutorCompletionService and the other thread management facilities in java.util.concurrent. You should not be managing threads manually in Java anymore, pretty much every case you can imagine is handled one or more of the ExecutorService implementations.