Android面试篇之ArrayList和LinkedList的区别

● 数据结构

ArrayList基于动态数组；LinkedList基于链表

● 随机访问

ArrayList优于LinkedList，因为LinkedList要移动指针来查找，下面以get方法为例

        //ArrayList的get方法，直接从数组中获取元素值        public E get(int index) {            if (index < 0 || index >= this.size)              throw new IndexOutOfBoundsException(outOfBoundsMsg(index));            if (ArrayList.this.modCount != this.modCount)                throw new ConcurrentModificationException();            return (E) ArrayList.this.elementData[offset + index];        }                        //LinkedList的get方法，node方法用来进行查找        public E get(int index) {             checkElementIndex(index);             return node(index).item;        }                        Node<E> node(int index) {            if (index < (size >> 1)) {//若index小于size的一半，则从头开始查找                Node<E> x = first;                for (int i = 0; i < index; i++)                    x = x.next;                return x;            } else {//若index大于size的一半，则从末尾向前开始查找                Node<E> x = last;                for (int i = size - 1; i > index; i--)                    x = x.prev;                return x;            }        }

● 插入删除

1. 末尾插入，两个的时间复杂度都是O(1)，所以差不多 [删除操作也同理]

            //ArrayList的add方法            public boolean add(E e) {                ensureCapacityInternal(size + 1);  // Increments modCount!!                elementData[size++] = e;                return true;            }                        //LinkedList的add方法            public boolean add(E e) {                linkLast(e);                return true;            }            void linkLast(E e) {                final Node<E> l = last;                final Node<E> newNode = new Node<>(l, e, null);                last = newNode;                if (l == null)                    first = newNode;                else                    l.next = newNode;                size++;                modCount++;            } 

2. 中间插入，时间复杂度也都是O(n)，所以也差不多 [删除操作也同理]

            //ArrayList的add方法            public void add(int index, E element) {                if (index > size || index < 0)                    throw new IndexOutOfBoundsException(outOfBoundsMsg(index));                ensureCapacityInternal(size + 1);  // Increments modCount!!                System.arraycopy(elementData, index, elementData, index + 1,                                 size - index);//index后面的元素后移，时间复杂度O(n)                elementData[index] = element;                size++;            }            //LinkedList的add方法            public void add(int index, E element) {                checkPositionIndex(index);                if (index == size) //index等于size时，直接链接到末尾                    linkLast(element);                else //否则直接将element链接到node(index)前面,node(index)的时间复杂度也是O(n)                    linkBefore(element, node(index));            }            void linkLast(E e) {                final Node<E> l = last;                final Node<E> newNode = new Node<>(l, e, null);                last = newNode;                if (l == null)                    first = newNode;                else                    l.next = newNode;                size++;                modCount++;            }            void linkBefore(E e, Node<E> succ) {                // assert succ != null;                final Node<E> pred = succ.prev;                final Node<E> newNode = new Node<>(pred, e, succ);                succ.prev = newNode;                if (pred == null)                    first = newNode;                else                    pred.next = newNode;                size++;                modCount++;            }