Am I doing it right?

[Slapy]

This are my two classes:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
public class Main {
 
    public static int number = 0;
 
    public static void main(String...args) {
        ExecutorService pool = Executors.newFixedThreadPool(3);
        while (number < 51) {
            for (int i = 0; i < 3; i++)
                pool.execute(new Counter(i));
        }
        pool.shutdown();
    }
}
 
class Counter implements Runnable {
 
    private int number;
 
    public Counter(int number) {
        this.number = number;
    }
 
    @Override
    public void run() {
        synchronized (Main.class) {
            if (Main.number < 51) {
                System.out.println("Thread "+ number +":"+ Main.number);
                Main.number++;
            }
        }
    }
}

So this program will run and count from 0 to 50 by using three different threads. Is my code thread safe? Is there any better way how to write my code?

[Slapy]

So here is it after few changes I made:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;
 
public class Main {
 
    public static final AtomicInteger number = new AtomicInteger(0);
 
    public static void main(String...args) {
        ExecutorService pool = Executors.newFixedThreadPool(3);
        for (int i = 0; i < 3; i++)
            pool.execute(new Counter(i));
        pool.shutdown();
    }
}
 
class Counter implements Runnable {
 
    private int number;
 
    public Counter(int number) {
        this.number = number;
    }
 
    @Override
    public void run() {
        while (Main.number.intValue() < 49)
            synchronized (Main.number) {
                System.out.println("Thread " + number + ":" + Main.number.getAndIncrement());
            }
    }
}

[Norm]

Does the code execute and do what you want?

[Slapy]

Yes, I was just asking if there is any way how to do it better.

[Norm]

How do you expect the work to divided amongst the three threads? Does the code show show any spreading of the work?

[Slapy]

It is just simpl program that have to count form 0 to 50 and to do so have to use 3 threads and output have to be:

Thread 1: 0
Thread 0: 1
Thread 2: 2
Thread 2: 3
Thread 1: 4
...
Thread 0: 50

it does not matter on order of threads.

[Norm]

What program are you executing for that output? The posted one has 3: 0->2,
the output you show has 4: 0->3

When I execute the code, 90% of the output is for thread 0. Sometimes thread 2 does nothing.

[Slapy]

oh am so sorry. I messed it up. It should be just 3 threads not 4 and it is just luck which thread will be selected. For example this is one of my outputs.

[Norm]

My question was if you are satisfied with a multithread demo program that only executes 1 thread.

[Slapy]

I think it should execute 3 threads:

for (int i = 0; i < 3; i++)
            pool.execute(new Counter(i));

or am I wrong?

--- Update ---

if you will try add after line with println Thread.sleep(10); surrounded with try/catch threads will have better chance to be switched.

[Norm]

As I said, the posted code executes one thread over 90% of the time. Often one of the threads is never executed.