Range Sum Query - Immutable

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.

Example:

Given nums = [-2, 0, 3, -5, 2, -1]

sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3

public class NumArray {
    private int[] sum_list;
    public NumArray(int[] nums) {
        sum_list = new int[nums.length];
        for(int i = 0; i<nums.length;i++){
            if(i == 0) sum_list[0] = nums[0];
            else sum_list[i] = nums[i] + sum_list[i-1];
        }
    }

    public int sumRange(int i, int j) {
        if(i == 0) return sum_list[j];
        else return sum_list[j] - sum_list[i-1];
    }
}


// Your NumArray object will be instantiated and called as such:
// NumArray numArray = new NumArray(nums);
// numArray.sumRange(0, 1);
// numArray.sumRange(1, 2);