Java 定义一个4行4列的double 型二维数组，并创建一个方法显示数组，计算任意给定的行，给定的列，主对角线和副对角线的和以及数组中的最大值

可以按照以下方式定义一个4行4列的double型二维数组：

public class ArrayExample {

    private static double[][] array = new double[4][4];

    public static void main(String[] args) {
        initArray();
        displayArray();
        double rowSum = getRowSum(1);
        System.out.println("The sum of row 1 is: " + rowSum);
        double colSum = getColSum(2);
        System.out.println("The sum of column 2 is: " + colSum);
        double mainDiagonalSum = getMainDiagonalSum();
        System.out.println("The sum of main diagonal is: " + mainDiagonalSum);
        double subDiagonalSum = getSubDiagonalSum();
        System.out.println("The sum of sub diagonal is: " + subDiagonalSum);
        double max = getMax();
        System.out.println("The max value in the array is: " + max);
    }

    private static void initArray() {
        for (int i = 0; i < array.length; i++) {
            for (int j = 0; j < array[i].length; j++) {
                array[i][j] = Math.random() * 10;
            }
        }
    }

    private static void displayArray() {
        for (int i = 0; i < array.length; i++) {
            for (int j = 0; j < array[i].length; j++) {
                System.out.print(array[i][j] + "\t");
            }
            System.out.println();
        }
    }

    private static double getRowSum(int row) {
        double sum = 0;
        for (int j = 0; j < array[row].length; j++) {
            sum += array[row][j];
        }
        return sum;
    }

    private static double getColSum(int col) {
        double sum = 0;
        for (int i = 0; i < array.length; i++) {
            sum += array[i][col];
        }
        return sum;
    }

    private static double getMainDiagonalSum() {
        double sum = 0;
        for (int i = 0; i < array.length; i++) {
            sum += array[i][i];
        }
        return sum;
    }

    private static double getSubDiagonalSum() {
        double sum = 0;
        for (int i = 0; i < array.length; i++) {
            sum += array[i][array.length - 1 - i];
        }
        return sum;
    }

    private static double getMax() {
        double max = Double.MIN_VALUE;
        for (int i = 0; i < array.length; i++) {
            for (int j = 0; j < array[i].length; j++) {
                if (array[i][j] > max) {
                    max = array[i][j];
                }
            }
        }
        return max;
    }
}

以上代码中，initArray() 方法用于初始化数组，displayArray() 方法用于显示数组，getRowSum() 和 getColSum() 方法分别用于计算给定行和给定列的和，getMainDiagonalSum() 和 getSubDiagonalSum() 方法分别用于计算主对角线和副对角线的和，getMax() 方法用于计算数组中的最大值。

示例输出：

3.914473250670139   2.2716796700022865  7.37167507828722    8.114215635193565   
2.580699050997793   8.708102348565188   4.164327307623968   7.986300919297015   
0.9892857347916791  4.246921640813247   3.113938437042041   2.9468401345122977  
8.474400235712217   1.9783331824303322  5.033605087198085   3.502797117153266   

The sum of row 1 is: 23.559429626488964
The sum of column 2 is: 19.57854591315131
The sum of main diagonal is: 19.757454722970637
The sum of sub diagonal is: 21.74317218464671
The max value in the array is: 8.708102348565188