java中双向链表的增、删、查操作

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import java.util.NoSuchElementException;   public class DoublyLinkedListImpl<E> {       private Node head;// sentinel before first item     private Node tail;// sentinel after last item     private int size;// number of elements on list       public DoublyLinkedListImpl() {         size = 0;     }       /**      * this class keeps track of each element information      *      * @author java2novice      *      */     private class Node {         E element;         Node next;         Node prev;           public Node(E element, Node next, Node prev) {             this.element = element;             this.next = next;             this.prev = prev;         }     }       /**      * returns the size of the linked list      *      * @return      */     public int size() {         return size;     }       /**      * return whether the list is empty or not      *      * @return      */     public boolean isEmpty() {         return size == 0;     }       /**      * adds element at the starting of the linked list      *      * @param element      */     public void addFirst(E element) {         Node tmp = new Node(element, head, null);         if (head != null) {             head.prev = tmp;         }// 跟原来的头节点交换位置         head = tmp;         if (tail == null) {             tail = tmp;         }// 首次添加节点的时候，头节点就是尾节点         size++;         System.out.println("adding: " + element);     }       /**      * adds element at the end of the linked list      *      * @param element      */     public void addLast(E element) {         Node tmp = new Node(element, null, tail);         if (tail != null) {             tail.next = tmp;         }// 跟原来的尾节点交换位置         tail = tmp;         if (head == null) {             head = tmp;         }// 首次添加节点的时候，头节点就是尾节点         size++;         System.out.println("adding: " + element);     }       /**      * get element at the specified location of the linked list      *      * @param loc      */     public Node getElement(int loc) {         Node tmp = head;         int index = 0;         while (loc != index) {             tmp = tmp.next;             index++;         }         return tmp;     }       /**      * add element at the specified location of the linked list      *      * @param element      * @param loc      */     public void insertAfterElement(E element, int loc) {         if (loc == size) {             addLast(element);         }         if (loc == 0) {             addFirst(element);         }         Node preEle = getElement(loc);         Node nextEle = preEle.next;         Node tmp = new Node(element, null, preEle);         // preEle=tmp.prev;//这一行没必要,因为创建类的时候已经指定preEle         preEle.next = tmp;         nextEle.prev = tmp;         tmp.next = nextEle;         size++;         System.out.println("inserting: " + element);     }       /**      * this method walks forward through the linked list      */     public void iterateForward() {           System.out.println("iterating forward..");         Node tmp = head;         while (tmp != null) {             System.out.println(tmp.element);             tmp = tmp.next;         }     }       /**      * this method walks backward through the linked list      */     public void iterateBackward() {           System.out.println("iterating backword..");         Node tmp = tail;         while (tmp != null) {             System.out.println(tmp.element);             tmp = tmp.prev;         }     }       /**      * this method removes element from the start of the linked list      *      * @return      */     public E removeFirst() {         if (size == 0)             throw new NoSuchElementException();         Node tmp = head;         head = head.next;         head.prev = null;         size--;         System.out.println("deleted: " + tmp.element);         return tmp.element;     }       /**      * this method removes element from the end of the linked list      *      * @return      */     public E removeLast() {         if (size == 0)             throw new NoSuchElementException();         Node tmp = tail;         tail = tail.prev;         tail.next = null;         size--;         System.out.println("deleted: " + tmp.element);         return tmp.element;     }       /**      * removes element from the specified location of the linked list      *      * @return      */     public E removeByIndex(int loc) {         Node tmp = null;         if (loc >= size || loc < 0) {             throw new NoSuchElementException();         } else if (loc == 0) {             removeFirst();         } else if (loc == size - 1) {             removeLast();         } else {             tmp = getElement(loc);             Node preEle = tmp.prev;             Node nextEle = tmp.next;             preEle.next = nextEle;             nextEle.prev = preEle;             size--;             System.out.println("deleted: " + tmp.element);             return tmp.element;         }         return null;     }       public static void main(String a[]) {           DoublyLinkedListImpl<Integer> dll = new DoublyLinkedListImpl<Integer>();         dll.addFirst(10);         dll.addFirst(34);         dll.addLast(56);         dll.addLast(364);         dll.insertAfterElement(88, 2);         dll.insertAfterElement(99, 3);         dll.iterateForward();         dll.removeByIndex(4);         dll.iterateBackward();     }   }