参考答案
ArrayList和LinkedList的区别：
- ArrayList 基于动态数组实现的非线程安全的集合；LinkedList 基于双向链表实现的非线程安全的集合；
- ArrayList比LinkedList更节约内存，因为LinkedList为每一个节点存储了两个引用节点，一个指向前一个元素，一个指向下一个元素；
- 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；LinkedList 的空间花费则体现在它的每一个元素都需要消耗存储指针节点对象的空间；
- 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；
- 扩容问题：ArrayList 使用数组实现，无参构造函数默认初始化长度为 10，数组扩容是会将原数组中的元素重新拷贝到新数组中，长度为原来的 1.5 倍(扩容代价高)；LinkedList 不存在扩容问题，新增元素放到集合尾部，修改相应的指针节点即可；
- 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，只需要修改节点指针即可；
- LinkedList 集合不支持高效的随机访问（RandomAccess）。
实例：
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));
}
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
以上，是Java面试题【ArrayList和LinkedList的区别的参考答案。
输出，是最好的学习方法。
欢迎在评论区留下你的问题、笔记或知识点补充~
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