Rotate int matrix by 90 degrees

MatrixRotator.java

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Scanner;

public class MatrixRotator {

    public static void main(String[] args) throws IOException {
        new MatrixRotator().rotate90(new FileInputStream("test.txt"), System.out);
    }

    public void rotate90(InputStream in, OutputStream out) throws IOException {
        final int m[][] = readMatrix(in);
        rotate90(m);
        print(m, out);
    }

    /* Rotation */

    private void rotate90(int m[][]) {
        final int dim = m.length;
        for (int n = 0; n < dim; n++) {
            rotate90(m, n, dim - n, n, dim - n);
        }
    }

    private void rotate90(int m[][], int minY, int maxY, int minX, int maxX) {
        assert (maxX < minX);
        assert (maxY < minY);

        final int length = maxX - minX;
        for (int i = 0; i < length - 1; i++) {
            final int tmp = m[minY][minX + i];

            m[minY][minX + i] = m[maxY - i - 1][minX];
            m[maxY - i - 1][minX] = m[maxY - 1][maxX - i - 1];
            m[maxY - 1][maxX - i - 1] = m[minY + i][maxX - 1];
            m[minY + i][maxX - 1] = tmp;
        }
    }

    /* IO utilities */

    private int[][] readMatrix(InputStream in) {
        final Scanner s = new Scanner(in);

        final int dim = s.nextInt();
        final int matrix[][] = new int[dim][dim];

        for (int i = 0; i < dim; i++) {
            for (int j = 0; j < dim; j++) {
                matrix[i][j] = s.nextInt();
            }
        }

        return matrix;
    }

    private void print(int matrix[][], OutputStream out) {
        final PrintWriter p = new PrintWriter(out);
        final int dim = matrix.length;
        for (int i = 0; i < dim; i++) {
            for (int j = 0; j < dim; j++) {
                p.print(matrix[i][j] + " ");
            }
            p.println();
        }

        p.flush();
    }
}