209 Minimum Size subarray sum

public class Solution {
    public int minSubArrayLen(int s, int[] nums) {
        if (nums == null || nums.length == 0) {
            return 0;
        }
        int len = nums.length;
        int start = 0;
        int end= 0;
        int min_Len = len + 1;
        int sum = 0;
        while (end < len) {
            while (sum < s && end < len ) {
                sum += nums[end];
                end++;
            }
            while (sum >= s && start < end) {
                if (end - start < min_Len) {
                    min_Len = end - start;
                }
                sum -= nums[start];
                start++;
            }
        }
        return min_Len < len+1 ? min_Len : 0;
    }
}