Arraylist 和 Linkedlist 的区别

首先我们摘录JDK的 java.util包中对于这两个类的部分定义

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;    /**     * Constructs an empty list with the specified initial capacity.     *     * @param  initialCapacity  the initial capacity of the list     * @throws IllegalArgumentException if the specified initial capacity     *         is negative     */    public ArrayList(int initialCapacity) {        if (initialCapacity > 0) {            this.elementData = new Object[initialCapacity];        } else if (initialCapacity == 0) {            this.elementData = EMPTY_ELEMENTDATA;        } else {            throw new IllegalArgumentException("Illegal Capacity: "+                                               initialCapacity);        }    }

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() {    }  }

从此可以看到两者都实现了List接口，而且都不是线程安全的。

两者的区别如下：

1.从底层实现上来说：ArrayList是实现了基于动态数组的数据结构，LinkedList基于链表的数据结构。
2.对于随机访问和修改操作，ArrayList性能优于LinkedList，因为LinkedList如果要查找某个元素，每次都是从否开始查找；而对于随机插入和删除操作，LinkedList性能优于ArrayList，因为ArrayList的插入和删除操作要移动后面的数据。

因为两个类都不是线程安全的，所以当有多个线程要同时获得类的实例的时候，可以通过Collections的静态方法，在外部给实例对象进行同步：
List list = Collections.synchronizedList(new ArrayList(…));
List list = Collections.synchronizedList(new LinkedList(…));

好了，现在再P一段连个类常用的方法吧，摘自API：

boolean add(E e)Appends the specified element to the end of this list.

void    add(int index, E element)Inserts the specified element at the specified position in this list.

boolean contains(Object o)Returns true if this list contains the specified element.

E   get(int index)Returns the element at the specified position in this list.

boolean isEmpty()Returns true if this list contains no elements.

E   remove(int index)Removes the element at the specified position in this list.

boolean remove(Object o)Removes the first occurrence of the specified element from this list, if it is present.

E   set(int index, E element)Replaces the element at the specified position in this list with the specified element.

int size()Returns the number of elements in this list.