Java: Print 2D Matrix

Quick and dirty one-liner

int[][] matrix = {
    {   5,   8,   13 },
    { -21,  34,   55 },
    {  89, 144, -233 }
};

System.out.println(Arrays.deepToString(matrix));

[[5, 8, 13], [-21, 34, 55], [89, 144, -233]]

With new lines

for (int[] row : matrix) {
    System.out.println(Arrays.toString(row));
}

[5, 8, 13]
[-21, 34, 55]
[89, 144, -233]

Right justified (padded) columns

void printMatrix(int[][] matrix) {
    int cols = matrix[0].length;
    int[] colWidths = new int[cols];
    for (int[] row : matrix) {
        for (int c = 0; c < cols; c++) {
            int width = String.valueOf(row[c]).length();
            colWidths[c] = Math.max(colWidths[c], width);
        }
    }
    for (int[] row : matrix) {
        for (int c = 0; c < cols; c++) {
            String fmt = String.format("%s%%%dd%s",
                    c == 0 ? "|" : "  ",
                    colWidths[c],
                    c < cols - 1 ? "" : "|%n");
            System.out.printf(fmt, row[c]);
        }
    }
}

|  5    8    13|
|-21   34    55|
| 89  144  -233|

Decimal points aligned

void printMatrix(double[][] matrix) {
    int cols = matrix[0].length;
    int[] iWidths = new int[cols];
    int[] fWidths = new int[cols];
    for (double[] row : matrix) {
        for (int c = 0; c < cols; c++) {
            String[] parts = String.valueOf(row[c]).split("\\.");
            iWidths[c] = Math.max(iWidths[c], parts[0].length());
            fWidths[c] = Math.max(fWidths[c], parts[1].length());
        }
    }
    for (double[] row : matrix) {
        for (int c = 0; c < cols; c++) {
            String[] parts = String.valueOf(row[c]).split("\\.");
            int lp = iWidths[c] - parts[0].length();
            int rp = fWidths[c] - parts[1].length();
            String fmt = String.format("%s%%%ss%%s.%%s%%%ss%s",
                    c == 0 ? "|" : "  ",
                    lp == 0 ? "" : lp,
                    rp == 0 ? "" : rp,
                    c < cols - 1 ? "" : "|%n");
            System.out.printf(fmt, "", parts[0], parts[1], "");
        }
    }
}

|  5.55    8.333    13.555|
|-21.0    34.1      55.3  |
| 89.2   144.5    -233.3  |