pop()

/* Remove the top item from the stack, and return its data */
public Item pop() {
    if (isEmpty()) {                                                    // 1
        throw new IndexOutOfBoundsException("The stack is empty.");     // 1
    }                                                                   // 1
    Item item = top.data;                                               // 2
    top = top.next;                                                     // 3
    length--;                                                           // 4
    return item;                                                        // 5
}