PJ Lab 3

// KvadratnaMatrica
import java.io.IOException;

public interface KvadratnaMatrica {
    public abstract double det();
    public abstract void ucitaj() throws IOException;
    public abstract void stampaj();
    public abstract void uctaijIzFajla(String ImeFajla) throws IOException;
    public abstract void upisiUFajl(String ImeFajla) throws IOException;
}

// PunaMatrica
import java.io.*;

public class PunaMatrica implements KvadratnaMatrica {
    private int n;
    private double[][] mat;

    public PunaMatrica(int x) throws Exception{
        if (x <= 0 )
            throw new Exception("Vrste i kolone moraju imati vecu vrednost od 0!");
        n = x;
        mat = new double[n][n];
    }

    public double det() {
        if (n == 1) {
            return mat[0][0];
        }
        if (n == 2) {
            return mat[0][0] * mat[1][1] - mat[0][1] * mat[1][0];
        }
        double vrednost = 0;
        double znak = -1;
        for (int i = 0; i < n; i++) {
            double[][] temp = new double[n-1][n-1];
            int iP = -1;
            for (int iT = 0; iT < n; iT++) {
                if (iT == i)
                    continue;
                iP++;
                int jP = -1;
                for (int jT = 1; jT < n; jT++) {
                    jP++;
                    temp[iP][jP] = mat[iT][jT];
                }
            }
            znak = znak * -1;
            vrednost = vrednost + detGlavna(temp, n - 1) * znak * mat[i][0];

        }
        return vrednost;
    }

    private double detGlavna(double[][] matrica, int m) {
        if (m == 2) {
            return matrica[0][0] * matrica[1][1] - matrica[0][1] * matrica[1][0];
        }
        double vrednost = 0;
        double znak = -1;
        for (int i = 0; i < m; i++) {
            double[][] temp = new double[m-1][m-1];
            int iP = -1;
            for (int iT = 0; iT < m; iT++) {
                if (iT == i)
                    continue;
                iP++;
                int jP = -1;
                for (int jT = 1; jT < m; jT++) {
                    jP++;
                    temp[iP][jP] = matrica[iT][jT];
                }
            }
            znak = znak * -1;
            vrednost = vrednost + detGlavna(temp, m - 1) * znak * matrica[i][0];
        }
        return vrednost;
    }

    public void ucitaj() throws IOException {
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader bfr = new BufferedReader(isr);
        System.out.print("Unesite ");
        System.out.print(n);System.out.print("*");System.out.print(n);
        System.out.println(" elemenata:");
        String samoC;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                samoC = bfr.readLine();
                mat[i][j] = Double.valueOf(samoC);
            }
        }
    }

    public void stampaj() {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                System.out.print(mat[i][j]);
                System.out.print(" ");
            }
            System.out.println();
        }
    }

    public void uctaijIzFajla(String ImeFajla) throws IOException {
        FileInputStream fin = new FileInputStream(ImeFajla);
        DataInputStream din = new DataInputStream(fin);
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                mat[i][j] = din.readDouble();
            }
        }
        din.close();
        fin.close();
    }

    public void upisiUFajl(String imeFajla) throws IOException {
        FileOutputStream fos = new FileOutputStream(imeFajla);
        DataOutputStream dos = new DataOutputStream(fos);
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                dos.writeDouble(mat[i][j]);
            }
        }
        dos.close();
        fos.close();
    }

}

// main
import java.io.IOException;

public class mejn {

    public static void main(String[] args) throws Exception {
        try{
            KvadratnaMatrica k = new PunaMatrica(3);
            k.uctaijIzFajla("lezgo");
            k.stampaj();
            System.out.print(k.det());
    }
        catch (IOException e) {
            System.out.println(e);
        }
        catch (Exception e) {
            System.out.print(e);
        }
    }

}