Nested array references

Question

I'm currently learning Java online and am confused about the following code and what one of the elements in the array is evaluating to:

int[] a = new int[]{9, 8, 3, 1, 5, 4};

for (int i = 0; i < a.length; i++) {
    if (a[i] % 2 == 0) {
        a[i] += 1;
    } else if (a[i] < a.length) {
        a[i] += a[a[i]];
    }
}

I am looking at a[3] and the number that this evaluates to, and when I am debugging the code, my IDE is showing that a[a[i]] is evaluating to 9, which is where I'm a bit confused.

I thought that a[3] would equal 1 and then a[1] would equal 8, however this doesn't seem to be the case. Could anyone provide clarity as the JetBrains Academy course doesn't refer to this.

Answer 1

Note the first condition - if (a[i] % 2 == 0) {a[i] += 1;} - this causes even values to be incremented. Therefore a[1] is incremented from 8 to 9.

Now, when i==3, a[a[i]] is evaluated to a[1] which is equal to 9. Then you are adding it to the original value of a[3] (note the operator is +=, not =), so a[3] becomes 1 + 9, which is 10.