Problema 2

import java.io.*;
import java.util.*;

/*
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/**
 *
 * @author ArCiGo
 */
public class Problema2 {

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

        File f = null;
        FileReader fr = null;
        BufferedReader br = null;

        int fil = 0, col = 0;
        int matrixA[][], matrixB[][];

        try {
            f = new File("in.txt");
            fr = new FileReader(f);
            br = new BufferedReader(fr);

            String[] line = br.readLine().split(" ");
            fil = Integer.parseInt(line[0]);
            col = Integer.parseInt(line[1]);
            matrixA = new int[fil][col];
            matrixB = new int[fil][col];

            for (int i = 0; i < fil; i++) {
                String data[] = br.readLine().split(" ");
                for (int j = 0; j < data.length; j++) {
                    matrixA[i][j] = Integer.parseInt(data[j]);
                }
            }

            for (int i = 0; i < fil; i++) {
                String data[] = br.readLine().split(" ");
                for (int j = 0; j < data.length; j++) {
                    matrixB[i][j] = Integer.parseInt(data[j]);
                }
            }

            producto(matrixA, matrixB);

            fr.close();
        } catch (Exception ex) {
            System.err.println("Fail");
        }

    }

    public static int[][] producto(int matrixA[][], int matrixB[][]) throws IOException {

        File archivo = new File("out.txt");
        FileWriter fr = new FileWriter(archivo);
        BufferedWriter br = new BufferedWriter(fr);

        int matrixC[][] = new int[matrixA.length][matrixB.length];
        int acum = 0;

        for (int i = 0; i < matrixA.length; i++) {
            for (int j = 0; j < matrixB.length; j++) {
                acum = 0;
                for (int k = 0; k < matrixC.length; k++) {
                    acum += (matrixA[i][k] * matrixB[k][j]);
                }
                matrixC[i][j] = acum;
            }
        }

        for (int i = 0; i < matrixA.length; i++) {
            for (int j = 0; j < matrixC.length; j++) {
//                System.out.print(matrixC[i][j]+" ");
                br.write(matrixC[i][j]+" ");
            }
//            System.out.println("");
            br.newLine();
        }
        br.close();
        return matrixC;
    }
}