如果在Java中会超过数组的0索引，该如何跳转？

Question

Let's say that i have an array of int's in range 65-90. I'll randomly pick one of elements and add 10 to it. Is it possible that value, if cross range of 90 return to 65? For example - i take a 85 and add 10 to it. So it should be 95, but i want a 70.

Answer 1

You can do it by placing your value in the interval [0, high - low] by removing low to your value, then add the number you want to it, take the modulo of the sum, and finally add low back to get back in the range [low, high]

public static void main(String[] args) {
    int low = 65, high = 90;
    System.out.println(addWithinInterval(85, 10, low, high));
}

private static int addWithinInterval(int value, int add, int low, int high) {
    return (value - low + add) % (high - low + 1) + low;
}

Answer 2

I'll randomly pick one of elements and add 10 to it. Is it possible that value, if cross range of 90 return to 65?

Sure, the remainder operator will do that for you:

n = (n - 65) % (90 - 65) + 65;

Example ( live copy ):

int n = 85;
for (int x = 0; x < 10; ++x) {
    n += 10;
    n = (n - 65) % (90 - 65) + 65;
    System.out.println(n);
}

Or here on site: Java and JavaScript are different, but their % operators work the same, so:

 let n = 85; for (let x = 0; x < 10; ++x) { n += 10; n = (n - 65) % (90 - 65) + 65; console.log(n); }