CODEWITHSUNDEEP
parallel-processingjava-8
Guforu
Guforu

Reputation: 4023

what is a difference between parallel and sequential method in Java?

I try to code currently in Java 8. Yesterday I have found the next source with the examples from linear algebra. On the basis of the Matrix Vector multiplication (last example in the link) I coded my owner method for multiplication of matrices. My code is here:

import java.util.stream.IntStream;

public static void matrixMatrixProduct() {
    System.out.println("Matrix matrix mulptiplication");
    final int DIM1 = 15;
    final int DIM2 = 20;
    final int DIM3 = 2;

    int[][] a = new int[DIM1][DIM2];
    int[][] b = new int[DIM1][DIM3];
    int[][] c = new int[DIM3][DIM2];
    int counter = 1;
    for (int i =0; i < DIM1; i++) {
        for (int j =0; j < DIM3; j++) {
            b[i][j] = counter++;
        }
    }

    for (int i =0; i < DIM3; i++) {
        for (int j =0; j < DIM2; j++) {
            c[i][j] = counter++;
        }
    }

    System.out.println("");
    System.out.println("Print matrix b");
    System.out.println("");
    for (int i = 0; i < DIM1; i++) {
        for (int j = 0; j < DIM3; j++) {
            System.out.print(b[i][j] + " ");
        }
        System.out.print("\n");
    }
    System.out.println("");
    System.out.println("Print matrix c");
    System.out.println("");
    for (int i = 0; i < DIM3; i++) {
        for (int j = 0; j < DIM2; j++) {
            System.out.print(c[i][j] + " ");
        }
        System.out.print("\n");
    }

    IntStream.range(0, DIM1)
        .parallel()
        .forEach( (i) -> {
            IntStream.range(0,  DIM2)
            .sequential()
            .forEach( (j) -> { 
                IntStream.range(0, DIM3)
                .parallel()
                .forEach( (k) -> {
                    a[i][j] += b[i][k]*c[k][j]; 
                });
             });
          });

    System.out.println("");
    System.out.println("Print matrix a");
    System.out.println("");
    for (int i = 0; i < DIM1; i++) {
        for (int j = 0; j < DIM2; j++) {
            System.out.print(a[i][j] + " ");
        }
        System.out.print("\n");
    }

My question is, what is exactly the difference between parallel() and sequential() method by the calling of IntStream class? (Actually this is the most important part, where I do the multiplication explicitly). Based on this knowledge I want to know, what is a correct usage in the last IntStream calling. Currently I have defined in this place the method parallel(), but I'm not sure this is a right solution... Actually, if I change parallel() to sequential() I don't see any difference in the output.

Upvotes: 1

Views: 1081

Answers (1)

Shadowen
Shadowen

Reputation: 836

Parallel operations happen concurrently. This means that the elements of the stream may be processed simultaneously.

Sequential operations happen one at a time.

Changing from sequential() to parallel() has no impact on the result since your operations are state-independent, but may affect your run-time. However, if the operations your perform affect future operations, then you should consider using sequential().

I would assume you want matrix operations to happen in parallel, but I'm not too familiar with the math.

Link to the Javadoc, as referenced by @the8472.

Upvotes: 1

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