Sort/ Merge arrays using multi threading

Question

I'm trying to learn multi-threading but cant get the hang of it. I've an example here. The idea is to use two threads to sort the two arrays a and b and use another thread to merge the sorted arrays to array c. This is my code. I tried it with threads didnt work, so i've put up the code without the threads

public class Main {
  public static void main(String[] args){
    Random r = new Random(System.currentTimeMillis());
    int n = r.nextInt(101) + 50;
    int[] a = new int[n];
    for(int i = 0; i < n; i++)
      a[i] = r.nextInt(100);
    n = r.nextInt(101) + 50;
    int[] b = new int[n];
    for(int i = 0; i < n; i++)
      b[i] = r.nextInt(100);
    SortThread t1 = new SortThread(a);  
    SortThread t2 = new SortThread(b);  
    MergeThread m = new MergeThread(t1.get(),t2.get());
    System.out.println(Arrays.toString(m.get()));
  }
}

public class SortThread {
  int[] x; 

  public SortThread(int[] x){
    this.x = x;
    run();    
  }
    public void run(){
      sort(x);
  }

  private void sort(int[] x){
    for(int i = 0; i < x.length ; i++){
      int indexOfSmallest = findIndexOfSmallest(x, i);
      int t = x[i];
      x[i] = x[indexOfSmallest];
      x[indexOfSmallest] = t;
    }
  }

  private int findIndexOfSmallest(int[] a, int from){
    int indexOfSmallest = from;

    for(int i = from; i < a.length; i++)
      if(a[i] < a[indexOfSmallest])
        indexOfSmallest = i;
    return indexOfSmallest;
  }


  public int[] get(){
    return x;
  }
}

public class MergeThread {
  int[] a;
  int[] b;
  int[] c;

  public MergeThread(int[] a, int[] b){
    this.a = a;
    this.b = b;
    c = new int[a.length + b.length];
    run();      
  }
  public void run(){
    merge();
  }

  private void merge(){
    int aIndex = 0, bIndex = 0, cIndex = 0;
    while(aIndex < a.length && bIndex < b.length)
      if(a[aIndex] < b[bIndex])
        c[cIndex++] = a[aIndex++];
      else
        c[cIndex++] = b[bIndex++];

    while(aIndex < a.length)
      c[cIndex++] = a[aIndex++];

    while(bIndex < b.length)
      c[cIndex++] = b[bIndex++];
  }

  public int[] get(){
    return c;
  }
}

There are some answers to this question over here: stackoverflow.com/questions/35114028/… — Matt Timmermans
– Matt Timmermans, Commented Feb 8, 2016 at 4:43

KRam1802 · Accepted Answer · 2016-02-08 03:57:42Z

0

A thread should implement the interface runnable and should override the method run.

Please Read Complete reference JAVA, it has many good examples.

answered Feb 8, 2016 at 3:57

KRam1802

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4 Comments

Dave_30 Over a year ago

Thanks for the reply. I got that part. where I am falling short is not calling the run method explicitly.

KRam1802 Over a year ago

Yes you should initiate the thread. The thread does not inititate itself :)

Dave_30 Over a year ago

like I said I put up my code without the thread part just to show what I am going for. I get the "extends Thread/implements Runnable part." However still not getting the not calling the run method. any suggestions or a link to any examples is highly appreciated

KRam1802 Over a year ago

Like i mentioned even if you extend thread/implement runnable, the thread you are creating has to be started by a start method, which should be overrided again. public void start () { System.out.println("Starting " + threadName ); if (t == null) { t = new Thread (this, threadName); t.start (); } } After this new can create a new instance of your thread and start it . In your case It should be t1.start and t2.start

KRam1802 · Accepted Answer · 2016-02-08 04:30:35Z

0

Like i mentioned even if you extend thread/implement runnable, the thread you are creating has to be started by a start method, which should be overrided again.

 public void start () { System.out.println("Starting " + threadName ); if (t == null) { t = new Thread (this, threadName); t.start (); } }

After this new can create a new instance of your thread and start it . In your case It should be

  t1.start()
  t2.start()
  m.start()

answered Feb 8, 2016 at 4:30

KRam1802

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