Question

Okay so I am using the JavaMail library and I am trying to fetch certain message numbers. I want to do it efficiently and not have to loop twice over something… Anyways my question to you is: How can I create an array that starts at index x and ends at index x - 11 without looping?

Answer 1

If you want to create and populate an array, you have basically three options:

1. Write the values explicitly: int[] nums = new int[] { 0, 1, 2, 3, 4, ... }

2. Use some form of for-loop: for (int i = 0; i < 10; i++) { nums[i] = i; }

3. Create it recursively:

int[] nums = new int[12];
nums = populate(0, x, nums);

private int[] populate(int index, int x, int[] nums) {
    if (nums.length >= index) {
        return nums;
    } else {
        nums[index] = x - index; // x-0 through x-11
        return populate(index+1, x, nums);
    }
}

Vanilla Java, without extra libraries and whatnot, doesn’t support a map function which would allow you to specify a function that would somehow auto-generate your values.

Though, I really don’t understand why you don’t want to use a loop, especially for something trivial like this.