Starting manual threads in main method

Question

I'm working with some low-level multithreading in java where I have two methods produce and consume:

public class Producer {

private LinkedList<Integer> list = new LinkedList();
private final int LIMIT = 10;
private Object lock = new Object();

public void produce() throws InterruptedException {

    int value = 0;

    while (true) {

        synchronized (lock) {

            // while loopet er til, for at blive ved med at tjekke at tjekke, at listen er fuld
            while (list.size() == LIMIT) {
                //notify vækker dette while-loop
                lock.wait(); //låsen venter indtil der er plads til at blive taget en ny værdi ud
                System.out.println("hej");
            }
            list.add(value++);
            lock.notify();
        }
    }
}

public void consume() throws InterruptedException {

    Random random = new Random();
    while (true) {
        synchronized (lock) {
            while (list.size() == 0) {
                lock.wait();
            }
            System.out.print("list size is " + list.size());
            int value = list.removeFirst();
            System.out.println("Current value is " + value);
            lock.notify();
        }

        Thread.sleep(random.nextInt(1000));

    }
  }
}

what can I put in the main method for the thread to run? Since I'm in the case is not using Thread of the Runnable interface, I can't start them, and instantiating an object, and calling the methods is not working?

To add to the other comment about using Runnable instead of extending a Thread: https://stackoverflow.com/questions/541487/implements-runnable-vs-extends-thread — John H, Aug 28 '18 at 03:32
@MickMnemonic it was just practise to understand the underlying principles of multithreading better, not for an actual application — Kristoffer Tølbøll, Aug 28 '18 at 07:04

score 1 · Accepted Answer · answered Aug 27 '18 at 20:36

You can use Anonymous Threads for doing this.

public static void main(String args[]) throws IOException, SaxonApiException {
    Producer producer = new Producer();
    new Thread()
    {
        public void run() {
            try {
                producer.consume();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }.start();

    new Thread()
    {
        public void run() {

            try {
                producer.produce();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }.start();
}

And what I am getting in the output is this.

list size is 1Current value is 0
list size is 10Current value is 1
hej
list size is 10Current value is 2
hej
list size is 10Current value is 3
hej
list size is 10Current value is 4
hej

Alexei Kaigorodov · Answer 2 · 2018-08-28T04:44:59.537

I assume both methods are in class Producer. No other classes are necessary.

public static void main(String... args) {
    Producer producer = new Producer();
    Thread t1 = new Thread(producer::produce);
    Thread t2 = new Thread(producer::consume);
    t1.start(); t2.start();
}

But first throws InterruptedException must be removed from the signatures of produce and consume methods. Throwing exception from the root method of a thread has no sense anyway, because there is no caller who can catch and react to that exception. Just catch the exception inside the methods, print stacktrace and return.

score -1 · Answer 3 · answered Aug 27 '18 at 20:33

To be able to run your methods simultaneously you will need to implement some variant of the thread class / runnable abstract as follows:

// Thread variant
class MultithreadingObject extends Thread{
    public void run(){
        print("...");
    }
} 

public static void main(string[] args){
   threadOne = new MultithreadingObject();
   threadTwo = new MultithreadingObject();
   // Run both threads
   threadOne.start();
   threadTwo.start();
}

Implements Runnable variant:

public class MyThread extends Thread {
    public MyThread() {
        super("MyThread");
    }
    public void run() {
        //Code
    }
}
public static void main(string[] args){
  threadOne = new MyThread();
  threadTwo = new MyThread();
  // Run both threads
  threadOne.start();
  threadTwo.start();
}

Starting manual threads in main method

3 Answers3