ArrayList和LinkedList的区别是什么？
- ArrayList基于动态数组实现的非线程安全的集合；LinkedList基于链表实现的非线程安全的集合。
- 对于随机index访问的get和set方法，一般ArrayList的速度要优于LinkedList。因为ArrayList直接通过数组下标直接找到元素；LinkedList要移动指针遍历每个元素直到找到为止。
- 新增和删除元素，一般LinkedList的速度要优于ArrayList。因为ArrayList在新增和删除元素时，可能扩容和复制数组；LinkedList实例化对象需要时间外，只需要修改指针即可。
- LinkedList集合不支持 高效的随机随机访问（RandomAccess）
- ArrayList的空间浪费主要体现在在list列表的结尾预留一定的容量空间，而LinkedList的空间花费则体现在它的每一个元素都需要消耗相当的空间
测试代码
public static void main(String[] args) { ArrayList<Integer> arrayList = new ArrayList<Integer>(); LinkedList<Integer> linkedList = new LinkedList<Integer>(); int size = 10000 * 1000; int index = 5000 * 1000; System.out.println("arrayList add " + size); addData(arrayList, size); System.out.println("linkedList add " + + size); addData(linkedList, size); System.out.println(); System.out.println("arrayList get " + index + " th"); getIndex(arrayList, index); System.out.println("linkedList get " + index + " th"); getIndex(linkedList, index); System.out.println(); System.out.println("arrayList set " + index + " th"); setIndex(arrayList, index); System.out.println("linkedList set " + index + " th"); setIndex(linkedList, index); System.out.println(); System.out.println("arrayList add " + index + " th"); addIndex(arrayList, index); System.out.println("linkedList add " + index + " th"); addIndex(linkedList, index); System.out.println(); System.out.println("arrayList remove " + index + " th"); removeIndex(arrayList, index); System.out.println("linkedList remove " + index + " th"); removeIndex(linkedList, index); System.out.println(); System.out.println("arrayList remove Object " + index); removeObject(arrayList, (Object)index); System.out.println("linkedList remove Object " + index); removeObject(linkedList, (Object)index); System.out.println(); System.out.println("arrayList add"); add(arrayList); System.out.println("linkedList add"); add(linkedList); System.out.println(); System.out.println("arrayList foreach"); foreach(arrayList); System.out.println("linkedList foreach"); foreach(linkedList); System.out.println(); System.out.println("arrayList forSize"); forSize(arrayList); System.out.println("linkedList forSize"); // forSize(linkedList); System.out.println("cost time: ..."); System.out.println(); System.out.println("arrayList iterator"); ite(arrayList); System.out.println("linkedList iterator"); ite(linkedList); } private static void addData(List<Integer> list, int size) { long s1 = System.currentTimeMillis(); for (int i = 0; i <size; i++) { list.add(i); } long s2 = System.currentTimeMillis(); System.out.println("cost time: " + (s2-s1)); } private static void getIndex(List<Integer> list, int index) { long s1 = System.currentTimeMillis(); list.get(index); long s2 = System.currentTimeMillis(); System.out.println("cost time: " + (s2-s1)); } private static void setIndex(List<Integer> list, int index) { long s1 = System.currentTimeMillis(); list.set(index, 1024); long s2 = System.currentTimeMillis(); System.out.println("cost time: " + (s2-s1)); } private static void addIndex(List<Integer> list, int index) { long s1 = System.currentTimeMillis(); list.add(index, 1024); long s2 = System.currentTimeMillis(); System.out.println("cost time: " + (s2-s1)); } private static void removeIndex(List<Integer> list, int index) { long s1 = System.currentTimeMillis(); list.remove(index); long s2 = System.currentTimeMillis(); System.out.println("cost time: " + (s2-s1)); } private static void removeObject(List<Integer> list, Object obj) { long s1 = System.currentTimeMillis(); list.remove(obj); long s2 = System.currentTimeMillis(); System.out.println("cost time: " + (s2-s1)); } private static void add(List<Integer> list) { long s1 = System.currentTimeMillis(); list.add(1024); long s2 = System.currentTimeMillis(); System.out.println("cost time: " + (s2-s1)); } private static void foreach(List<Integer> list) { long s1 = System.currentTimeMillis(); for (Integer i : list) { //do nothing } long s2 = System.currentTimeMillis(); System.out.println("cost time: " + (s2-s1)); } private static void forSize(List<Integer> list) { long s1 = System.currentTimeMillis(); int size = list.size(); for (int i = 0; i <size; i++) { list.get(i); } long s2 = System.currentTimeMillis(); System.out.println("cost time: " + (s2-s1)); } private static void ite(List<Integer> list) { long s1 = System.currentTimeMillis(); Iterator<Integer> ite = list.iterator(); while (ite.hasNext()) { ite.next(); } long s2 = System.currentTimeMillis(); System.out.println("cost time: " + (s2-s1)); }
JDK1.8，win7 64位。结果
arrayList add 10000000 cost time: 3309 linkedList add 10000000 cost time: 1375 arrayList get 5000000 th cost time: 0 linkedList get 5000000 th cost time: 53 arrayList set 5000000 th cost time: 0 linkedList set 5000000 th cost time: 44 arrayList add 5000000 th cost time: 3 linkedList add 5000000 th cost time: 45 arrayList remove 5000000 th cost time: 3 linkedList remove 5000000 th cost time: 46 arrayList remove Object 5000000 cost time: 31 linkedList remove Object 5000000 cost time: 131 arrayList add cost time: 0 linkedList add cost time: 0 arrayList foreach cost time: 30 linkedList foreach cost time: 128 arrayList forSize cost time: 5 linkedList forSize cost time: ... arrayList iterator cost time: 6 linkedList iterator cost time: 113
思考：
- arrayList add 10000000 cost time: 3293；linkedList add 10000000 cost time: 1337
- arrayList add 1000000 cost time: 22 ； linkedList add 1000000 cost time: 1011
- 跑另外一组数据，size设为1000 * 1000，得出当size增加，ArrayList的add操作的累计时间增长更快
- 千万别在循环中调用LinkedList的get方法，耗时会让你崩溃
- 代码例子中，"新增和删除元素，一般LinkedList的速度要优于ArrayList"并不成立，可以思考一下原因。
源码分析参考：
