JavaSection1061

// Guide to Java
// Copyright 2014, by J.T. Streib and T. Soma

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

public class MatrixMult {
public static void main(String[] args) throws IOException {

    // declaration and initialization of variables
    int[][] matrix1, matrix2, matrix3;
    int i, j;
    String fileName;
    Scanner scanner, inFile;
    PrintWriter outFile;

    matrix1 = new int[2][2];
    matrix2 = new int[2][2];
    matrix3 = new int[2][2];

    scanner = new Scanner(System.in);
    System.out.print("Enter filename: ");
    fileName = scanner.next();

    // open input file
    inFile = new Scanner(new File(fileName));

    // read two matrices from file
    for(i=0; i<2; i++)
       for(j=0; j<2; j++)
          matrix1[i][j] = inFile.nextInt();
    for(i=0; i<2; i++)
       for(j=0; j<2; j++)
          matrix2[i][j] = inFile.nextInt();

    // close input file
    inFile.close();

    // matrix multiplication
    for(i=0; i<2; i++)
       for(j=0; j<2; j++)
          matrix3[i][j] = matrix1[i][0]*matrix2[0][j]
                        + matrix1[i][1]*matrix2[1][j];

    // open output file
    outFile = new PrintWriter(new FileWriter(fileName, true));

    // append result to output file
    outFile.println();
    for(i=0; i<2; i++) {
       for(j=0; j<2; j++)
          outFile.print(matrix3[i][j] + " ");
       outFile.println();
    }

    // close output file
    outFile.close();
}
}