1. 双向链表

1.1 概念

双向链表也叫双链表，是链表的一种，它的每个数据结点中都有两个指针，分别指向直接后继和直接前驱。所以，从双向链表中的任意一个结点开始，都可以很方便地访问它的前驱结点和后继结点。

1.2 实例

BookNode.java

package data_structure;

public class BookNode {

    public int id;

    public String name;

    public double price;

    //节点下一个节点  直接后继
    public BookNode next;

    //上一个节点   直接前驱
    public BookNode pre;

    public BookNode(int id, String name, double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }

    @Override
    public String toString() {
        return "BookNode{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", price=" + price +
                '}';
    }
}

DualLinkedList.java

package data_structure;

public class DualLinkedList {
    private final BookNode head = new BookNode(0, "", 0.0);

    /**
     * 添加结尾新的节点
     */
    public void addLast(BookNode newNode) {
        BookNode temp = head;

        while (temp.next != null) {

            //如果第一次进来则进入，表示双向链表是空数据

            temp = temp.next;
        }
        /*
         * 需要把新的节点给上一个节点
         * 需要把上一个节点next指向新的节点
         */
        temp.next = newNode;
        newNode.pre = temp;


    }

    /**
     * 修改节点
     * 条件：双向链表中的每一个结点的id和修改的id对比，如果对比成功，则进行修改该结点
     * ，如果没有对比成功，双向链表中未找到目标结点
     */
    public void updateNode(BookNode node) {
        //是否是空链表
        if (head.next == null) {
            System.out.println("空链表...");
            return;
        }

        BookNode temp = head.next;

        boolean flg = false;
        while (true) {
            if (temp == null) {
                break;
            }
            if (temp.id == node.id) {
                flg = true;
                break;
            }
            temp = temp.next;
        }
        if (flg) {
            temp.name = node.name;
            temp.price = node.price;
        } else {
            System.out.println("未找到要修改的节点...");
        }
    }

    /**
     * 双向链表删除
     * 条件：根据id编号进行删除节点
     */
    public void delNode(int id) {
        if (head.next == null) {
            System.out.println("空链表...");
            return;
        }

        BookNode temp = head.next;
        boolean flg = false;
        while (true) {
            if (temp == null) {
                break;
            }
            if (temp.id == id) {
                flg = true;
                break;
            }
            temp = temp.next;
        }
        if (flg) {
            temp.pre.next = temp.next;
            if (temp.next != null) {
                temp.next.pre = temp.pre;
            }
        } else {
            System.out.println("未找到该结点...");
        }
    }

    public void list() {
        BookNode tempNode = head.next;
        while (tempNode != null) {
            System.out.println(tempNode.toString());
            tempNode = tempNode.next;
        }
    }
}

LinkedTest.java

package data_structure;

/**
 * @company: 北京动力节点
 * @author:韩国庆
 */
public class LinkedTest {

    public static void main(String[] args) {

        DualLinkedList dualLinkedList = new DualLinkedList();

        BookNode bookNode1 = new BookNode(1, "红楼梦", 66.00);
        BookNode bookNode2 = new BookNode(2, "西游记", 66.00);
        BookNode bookNode3 = new BookNode(3, "水浒传", 66.00);
        BookNode bookNode4 = new BookNode(4, "三国演义", 66.00);

        dualLinkedList.addLast(bookNode1);
        dualLinkedList.addLast(bookNode2);
        dualLinkedList.addLast(bookNode3);
        dualLinkedList.addLast(bookNode4);
        dualLinkedList.list();
        dualLinkedList.delNode(1);
        System.out.println("------------------------------------------");
        dualLinkedList.updateNode(new BookNode(3, "计算机", 66.00));
        dualLinkedList.list();
    }

}

运行结果：