Shift, copy, swap

Shifting and inserting — the exam's hardest array operations. To remove the element at index k (keeping order), shift everything after it left:

// {a, b, c, d} remove index 1 → {a, c, d, ?}
for (int i = k; i < arr.length - 1; i++) {
    arr[i] = arr[i + 1];
}

The loop bound length - 1 is the crux: on the last pass, arr[i + 1] is the final element — one past that would be out of bounds. The last slot now holds a duplicate; track a logical size separately when needed.

Copying: copy = original; copies the reference, not the values — both names then mutate one array. The value copy needs a loop (or Arrays.copyOf):

int[] copy = new int[arr.length];
for (int i = 0; i < arr.length; i++) {
    copy[i] = arr[i];
}

Swapping two elements needs the three-line temp dance:

int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;

Forgetting the temp silently destroys one value — the classic bug the wrong solutions below commit.