LinkedList实现

JDK源码中只包含了一个header节点，各有利弊。

import java.util.Iterator;import java.util.NoSuchElementException;public class LinkedList<E> {public LinkedList() {clear();}/** * 清空链表 */public void clear() {this.head = new Node<E>(null, null, null);this.tail = new Node<E>(null, head, null);this.head.next = tail;this.size = 0;}/** * 返回链表大小 *  * @return 大小 */public int size() {return this.size;}/** * 链表是否为空 */public boolean isEmpty() {return size() == 0;}/** * 添加元素e，在末尾 */public boolean addLast(E e) {add(size(), e);return true;}public boolean addFirst(E e) {add(0, e);return true;}/** * 在index位置插入元素e */public void add(int index, E e) {addBefore(getNode(index), e);}/** * 获取index位置元素 */public E get(int index) {return getNode(index).data;}public E getFirst() {if (size() == 0) {throw new NoSuchElementException();}return head.next.data;}public E getLast() {if (size() == 0) {throw new NoSuchElementException();}return tail.prev.data;}public boolean contains(E e) {return indexOf(e) > 0;}public int indexOf(E e) {Node<E> p = head.next;int i = 0;while (p.next != null) {if (p.data.equals(e)) {return i;}p = p.next;i++;}return -1;}/** * 将index位置的元素设置为e */public E set(int index, E e) {Node<E> node = getNode(index);E oldValue = node.data;node.data = e;return oldValue;}/** * 移除idnex位置的元素 */public E remove(int index) {return remove(getNode(index));}public E removeFirst() {return remove(head.next);}public E removeLast() {return remove(tail.prev);}/** * 在p节点前添加元素e */private void addBefore(Node<E> p, E e) {Node<E> newNode = new Node<E>(e, p.prev, p);p.prev.next = newNode;p.prev = newNode;size++;}/** * 移除节点p */private E remove(Node<E> p) {p.next.prev = p.prev;p.prev.next = p.next;size--;return p.data;}/** * 获取index为位置的节点 */private Node<E> getNode(int index) {if (index < 0 || index > size) {throw new IndexOutOfBoundsException();}Node<E> p;if (index < (size >> 1)) {p = head.next;for (int i = 0; i < index; i++) {p = p.next;}} else {p = tail;for (int i = size(); i > index; i--) {p = p.prev;}}return p;}/** * 返回LinkedList迭代器 */public Iterator<E> iterator() {return new Iterator<E>() {private Node<E> current = head.next;private boolean canRemove = false;@Overridepublic boolean hasNext() {return current != tail;}@Overridepublic E next() {if (!hasNext()) {throw new NoSuchElementException();}E value = current.data;current = current.next;canRemove = true;return value;}@Overridepublic void remove() {if (!canRemove) {throw new IllegalStateException();}LinkedList.this.remove(current.prev);canRemove = true;}};}private int size;private Node<E> head;private Node<E> tail;private static class Node<E> {public E data;public Node<E> prev;public Node<E> next;public Node(E e, Node<E> prev, Node<E> next) {this.prev = prev;this.next = next;this.data = e;}}}

import static org.junit.Assert.*;import java.util.Iterator;import org.junit.Test;public class LinkedListTest {@Testpublic void testClear() {LinkedList<Integer> list = new LinkedList<Integer>();list.addLast(1);list.addLast(1);list.addLast(1);list.addLast(1);list.addLast(1);list.addLast(1);list.clear();int expectedSize = 0; assertEquals(expectedSize, list.size());}@Testpublic void testSize1() {LinkedList<Integer> list = new LinkedList<Integer>();int expected  = 0;assertEquals(expected, list.size());}@Testpublic void testSize2() {testClear();}@Testpublic void testIsEmpty() {LinkedList<Integer> list = new LinkedList<Integer>();boolean expected  = true;assertEquals(expected, list.isEmpty());}@Testpublic void testAddE() {LinkedList<Integer> list = new LinkedList<Integer>();list.addLast(1);list.addLast(1);list.addLast(1);list.addLast(1);list.addLast(1);list.addLast(1);int expected = 6;assertEquals(expected, list.size());}@Testpublic void testAddIntE() {LinkedList<Integer> list = new LinkedList<Integer>();list.add(0, 1);int expected = 1;assertEquals(expected, list.get(0).intValue());}@Testpublic void testGet() {LinkedList<Integer> list = new LinkedList<Integer>();list.addLast(1);list.addLast(2);list.addLast(3);list.addLast(4);list.addLast(5);list.addLast(6);int expected = 6;assertEquals(expected, list.get(5).intValue());}@Testpublic void testSet() {LinkedList<Integer> list = new LinkedList<Integer>();list.addLast(1);list.addLast(2);list.addLast(3);list.addLast(4);list.addLast(5);list.addLast(6);list.set(2,-1);assertEquals(-1, list.get(2).intValue());}@Testpublic void testRemove1() {LinkedList<Integer> list = new LinkedList<Integer>();list.addLast(1);list.addLast(2);list.addLast(3);list.addLast(4);list.addLast(5);list.addLast(6);list.remove(5);Iterator<Integer> itr = list.iterator();int i = 1;while(itr.hasNext()){assertEquals(i++, itr.next().intValue());}}@Testpublic void testRemove() {LinkedList<Integer> list = new LinkedList<Integer>();list.addLast(1);list.addLast(2);list.addLast(3);list.addLast(4);list.addLast(5);list.addLast(6);list.remove(5);Iterator<Integer> itr = list.iterator();int i = 1;while(itr.hasNext()){assertEquals(i++, itr.next().intValue());}}@Testpublic void testIterator() {LinkedList<Integer> list = new LinkedList<Integer>();list.addLast(1);list.addLast(2);list.addLast(3);list.addLast(4);list.addLast(5);list.addLast(6);Iterator<Integer> itr = list.iterator();int i = 1;while(itr.hasNext()){assertEquals(i++, itr.next().intValue());} }}