Mutli Threading Question Written - 1

Question : There are three threads, which can print an assigned array as below:

            Thread1  - {1,4,5}
            Thread2  - {2,5,7}       
            Thread3  - {3,6,9}

Write a program that print the output so that the output is always 1,2,3,4,5,6,7,8,9? Also, make it extendible so that the same logic can be applied to more number of threads.

Solution:

 

public class MultipleThreads {
       public static void main(String args[]) {
         //same instance of printer that is shared among the threads
         Printer printer = new Printer(3); // three is the maximum number of threads.
         
         NumberThread thread1 = new NumberThread(new Integer[]{1,4,7}, 1, printer); // First arguement is the array, second is the Thread number, printer is the shared instance
         NumberThread thread2 = new NumberThread(new Integer[]{2,5,8}, 2, printer);
         NumberThread thread3 = new NumberThread(new Integer[]{3,6,9}, 3, printer);

         thread1.start();
         thread2.start();
         thread3.start();

       }
} 

The NumberThread class looks like:

   public class NumberThread extends Thread {
       
        private Integer[] integerArray;
        private int threadNumber;
        private Printer printer;

        //Constructor
        public NumberThread(Integer[] array, int thread, Printer printer) {
               this.integerArray = array;
               this.threadNumber = thread;
               this.printer = printer;
        }

        @Override
        public void run() {
            int index = 0; // index to keep track that all the elements are traversed
            while(index < integerArray.length) {
                synchronized(printer) {
                   while(!printer.myTurn(this.threadNumber)) {
                        try {
                              printer.wait();
                        } catch (InterruptedException ie) {
                        }
                   }
                   printer.print(integerArray[index]);
                   index++;
                   printer.notifyAll();
                }
            }
        }

   }

The Printer class is as follows:

  public class Printer {
         private int maxThreads;
         private int currentThread = 1;
         
         public Printer(int numberOfThreads) {
           this.maxThreads = numberOfThreads;
         }

         public void print(int number) {
            // print the number
             System.out.println(number);
             currentThread = (currentThread % maxThreads) + 1;
         }

         public boolean myTurn(int threadNumber) {
             return currentThread == threadNumber;
         }
  }

In order to extend the above logic, it can be extended for the number of elements in array and the number of threads that needs to be executed in a one-one-by kind of execution.

Please leave a comment if you think there is a problem in the above code or if there is any modification / optimization that can be done.