Threads Interview Questions

“5. The user of this class expected the output “Num: 1000000”. They got something else. What went wrong and how would you fix it?

public class Test
{
    public final static int NUMTHREADS = 1000;
    public final static int NUMLOOP = 1000;
    public static int num = 0;

    static class Mythread extends Thread
    {
        @Override
        public void run()
        {
            for (int i = 0; i < NUMLOOP; i++)
            {
                ++num;
            }
        }
    }

    public static void main(String argv[])
    {
        Mythread threads[] = new Mythread[NUMTHREADS];
        for (int i = 0; i < NUMTHREADS; ++i)
        {
            threads[i] = new Mythread();
            threads[i].start();
        }

        try
        {
            for (int i = 0; i < NUMTHREADS; ++i)
            {
                threads[i].join();
            }
        }
        catch (InterruptedException e)
        {
        }
        System.out.println("Num: " + num);
    }
}”

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