Google - Largest Sum Submatrix

Given an NxN matrix of positive and negative integers, write code to find the submatrix with the largest possible sum.

// "static void main" must be defined in a public class.
public class Main {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

class Solution{
     public int maxSubMatrix(int[][] nums) {
         if(nums == null || nums.length == 0 || nums[0].length == 0){
             return 0;
         }
         int r = nums.length;
         int c = nums[0].length;
         int maxSum = nums[0][0];
         for(int i = 0; i < r; i++){
             int[] sum = new int[c];
             for(int j = i; j < r; j++){
                 for(int k = 0; k < c; k++){
                     sum [k] += nums[j][c];
                 }
                 int m = maxSubArray(sum);
                 maxSum = Math.max(maxSum, m);
             }
         }
     }

    public int maxSubArray(int[] nums) {
        if(nums == null || nums.length == 0){
            return 0;
        }
        int maxSoFar = nums[0];
        int maxEndingHere = nums[0];
        for(int i = 1; i < nums.length; i++){
            maxEndingHere = Math.max(maxEndingHere + nums[i], nums[i]);
            maxSoFar = Math.max(maxSoFar, maxEndingHere);
        }
        return maxSoFar;
    }
}