Question

java language question

Write a program that employs 2 threads that each toss their own die (modelled by a random number generator that generates random numbers in the range 1..6) a given number of times. In both cases the result of each toss is stored in a shared array. The array is deemed to be large enough to store the result of every throw and each thread should only write to its own array segment. Once the threads have completed their work then the main program counts the frequency of each number thrown and prints it on the screen.

Answer 1

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

// Threads.java

public class Threads {

      public static void main(String[] args) throws Exception {

            // number of throws

            int numThrows = 100000;

            // a shared array of numThrows size to store the thrown die rolls

            int sharedArray[] = new int[numThrows];

            // creating a DieRollThread, passing the array, 0 as start index, middle

            // index of sharedArray as end index (first half of the array)

            DieRollThread t1 = new DieRollThread(sharedArray, 0, numThrows / 2);

            // creating another DieRollThread to store the die rolls in second half

            // of the array

            DieRollThread t2 = new DieRollThread(sharedArray, (numThrows / 2) + 1,

                        numThrows - 1);

            // starting both threads

            t1.start();

            t2.start();

            // waiting for both threads to finish execution

            t1.join();

            t2.join();

            // creating an array to store the frequencies of each number. index 0

            // represents frequency of 1, index 5 represents frequency of 6 etc.

            int frequencies[] = new int[6];

            for (int i = 0; i < sharedArray.length; i++) {

                  // getting value of die at index i

                  int dieValue = sharedArray[i];

                  // incrementing the counter at dieValue-1 index

                  frequencies[dieValue - 1]++;

            }

            System.out.println("Frequencies of each number thrown:");

            int sum = 0;

            // now looping and printing frequency of each number

            for (int i = 0; i < frequencies.length; i++) {

                  System.out.println((i + 1) + ": " + frequencies[i]);

                  // summing the frequencies so that we can verify it with numRolls

                  sum += frequencies[i];

            }

            // if everything is correct, sum of frequencies will be equal to

            // numThrows

            System.out.println("Total throws: " + sum);

      }

}

// a class extending Thread class that performs rolling a die and storing the

// drawn number in an array at specified positions, should be placed within Threads.java file

class DieRollThread extends Thread {

      // reference to the array

      int[] array;

      // start and end index of segments alloted to this thread

      int startIndex, endIndex;

      // constructor receiving reference to the array, start and end index

      public DieRollThread(int[] array, int startIndex, int endIndex) {

            this.array = array;

            this.startIndex = startIndex;

            this.endIndex = endIndex;

      }

      @Override

      public void run() {

            // looping from i=startIndex to i=endIndex

            for (int i = startIndex; i <= endIndex; i++) {

                  // generating a random number between 1 and 6

                  int die = (int) (Math.random() * 6) + 1;

                  // adding to the array at index i

                  array[i] = die;

            }

      }

}

/*OUTPUT*/

Frequencies of each number thrown:

1: 16822

2: 16708

3: 16530

4: 16890

5: 16565

6: 16485

Total throws: 100000