一、他们底层的数据结构不同
ArrayList的底层是由数组实现的，可以通过源代码看出来：
public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable { private static final long serialVersionUID = 8683452581122892189L; /** * Default initial capacity. */ private static final int DEFAULT_CAPACITY = 10; /** * Shared empty array instance used for empty instances. */ private static final Object[] EMPTY_ELEMENTDATA = {}; /** * Shared empty array instance used for default sized empty instances. We * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when * first element is added. */ private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {}; /** * The array buffer into which the elements of the ArrayList are stored. * The capacity of the ArrayList is the length of this array buffer. Any * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA * will be expanded to DEFAULT_CAPACITY when the first element is added. */ transient Object[] elementData; // non-private to simplify nested class access /** * The size of the ArrayList (the number of elements it contains). * * @serial */ private int size;
LinkedList的底层是基于链表实现的，因为链表是由多个节点所构成的，链表的单元是节点，看一下源码：
public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable { transient int size = 0; /** * Pointer to first node. * Invariant: (first == null && last == null) || * (first.prev == null && first.item != null) */ transient Node<E> first; /** * Pointer to last node. * Invariant: (first == null && last == null) || * (last.next == null && last.item != null) */ transient Node<E> last; /** * Constructs an empty list. */ public LinkedList() { }
二、两个类实现了List接口，但是LinkedList还实现了Deque接口
ArrayList类实现了List接口，看一下源代码：
public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable { ................
LinkedList不但实现了List接口，还实现了Deque接口，所以他也可以作为双端队列来使用
public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable { ................
三、适用场景不同
ArrayList 底层是基于数组实现，所以查询相对比较快，
增加删除比较慢，因为可能会涉及到一个扩容的操作
public boolean add(E e) { linkLast(e); return true; }
LinkedList 底层基于链表实现，所以更加适合添加删除的操作
/** * Links e as last element. */ 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++; }
