LinkedList

LinkedList类是由链表实现的，这里我使用了双链表进行实现。在这里我们还有两个内部类：（1）Node类（用于记录节点的数据域，与其前驱元素和后继元素的引用）。（2）迭代器类

public class MyLinkedList<T> implements Iterable<T> {private int size;private int modCount=0;private Node<T> beginMarker;private Node<T> endMarker;public MyLinkedList() {doClear();}public void clear(){doClear();}public void doClear(){beginMarker = new Node<T>(null,null,null);endMarker = new Node<T>(null,beginMarker,null);beginMarker.next = endMarker;this.size = 0;this.modCount++;}public int size(){return this.size;}public boolean isEmpty(){return size==0;}public void add(int index,T element){addBefore(getNode(index),element);}public boolean add(T element){add(size,element);return true;}public T get(int index){return getNode(index).data;}public T set(int index,T element){Node<T> node = getNode(index);T oldElement = node.data;node.data = element;return oldElement;}public T remove(int index){return remove(getNode(index));}private T remove(Node<T> delNode){delNode.next.prev = delNode.prev;delNode.prev.next = delNode.next;size--;modCount++;return delNode.data;}private void addBefore(Node<T> p,T element){Node<T> newNode = new Node<T>(element,p.prev,p);newNode.prev.next = newNode;p.prev = newNode;this.size++;this.modCount++;}private Node<T> getNode(int index){Node<T> p;if(index>=0 && index<=size){if(index<(size/2)){p = beginMarker.next;for(int i=0;i<index;i++){p = p.next;}}else{p = endMarker;for(int i=size;i>index;i--){p = p.prev;}}}else{throw new IndexOutOfBoundsException();}return p;}@Overridepublic Iterator<T> iterator() {return new LinkedListIterator();}private static class Node<T>{public T data;public Node<T> prev;public Node<T> next;public Node(T data, Node<T> prev, Node<T> next) {this.data = data;this.prev = prev;this.next = next;}}private class LinkedListIterator implements Iterator<T>{private Node<T> current = beginMarker.next;private int expectedModCount = modCount;private boolean okToRemove = false;@Overridepublic boolean hasNext() {return current != endMarker;}@Overridepublic T next(){if(modCount != expectedModCount){throw new ConcurrentModificationException();}if(!hasNext()){throw new NoSuchElementException();}T n = current.data;current = current.next;okToRemove = true;return n;}public void remove(){if(modCount != expectedModCount){throw new ConcurrentModificationException();}if(!okToRemove){throw new IllegalStateException();}MyLinkedList.this.remove(current.prev);size--;expectedModCount++;okToRemove = false;}}}