Implementation of Java data structure doubly linked list

Doubly linked list

What is a doubly linked list?

Doubly linked list, also called doubly linked list, is a type of linked list. Each data node has two pointers, pointing to the direct successor and direct predecessor respectively. Therefore, starting from any node in the doubly linked list, you can easily access its predecessor nodes and successor nodes.

The main difference between a doubly linked list and a one-way linked list:

Search direction: The search direction of a one-way linked list can only be in one direction, while a doubly linked list can be forward or forward Look backwards.
Delete: Deletion of a one-way linked list requires the use of auxiliary pointers. First find the predecessor of the node to be deleted, and then delete it.
Temp.next = Temp.next.next; (TEMP is auxiliary pointer)
Bidirectional linked list can be deleted by themselves.

The advantages and disadvantages of doubly linked lists and singly linked lists:

Advantages: The doubly linked list structure is more advantageous than the singly linked list structure.

Disadvantages: From the storage structure point of view, the doubly linked list has one more pointer than the one-way linked list, requiring an additional, linear memory usage. (A pointer is 4 bytes in 32-bit operating systems and 8 bytes in 64-bit operating systems).

Illustration of the logical structure of a doubly linked list:

Specific operations of a doubly linked list:

Add:
Illustration:

Code:

//添加一个节点到最后
    public void add(DoubleNode newNode) {
        DoubleNode temp = head;
        while (true) {
            if (temp.next == null) {
                // 当temp.next 为空时，证明temp为最后一个元素。
                temp.next = newNode; //temp节点的下一位指向新节点
                newNode.pre = temp;//新节点的前一位指向temp
                //这两步构成双向链表
                break;
            }else if (temp.next.ID == newNode.ID) {
                //ID相同证明 已经存在该学生。
                System.out.printf("要插入学号为%d的学生已经存在。\n", newNode.ID);
                break;
            }
            temp = temp.next;
        }
    }
 
    //按学号顺序添加节点
    public void Sortadd(DoubleNode newNode) {
        DoubleNode temp = head;
        while (true) {
            if (temp.next == null) {
                //说明要添加的节点序号在当前链表中最大，因此直接添加在末尾。
                temp.next = newNode;//temp节点的下一位指向新节点
                newNode.pre = temp;//新节点的前一位指向temp
                //这两步构成双向链表
                break;
            } else if (temp.next.ID > newNode.ID) {
                //当前节点的下一位节点的编号大于 要添加的新节点，则证明新节点要添加在temp节点之后
                newNode.next = temp.next;//要添加节点的下一位 指向temp当前节点的下一位
                temp.next.pre = newNode;//temp当前节点的下一位的前一位 指向 新节点构成双向链表
                temp.next = newNode; // 再让当前节点的下一位指向 新节点
                newNode.pre = temp;//新节点的前一位 指向 当前节点temp
                //这样连接完成后就将  新节点插入 到 原本链表的temp节点与temp.next节点之间
                break;
            }else if (temp.next.ID == newNode.ID) {
                //ID相同证明 已经存在该学生。
                System.out.printf("要插入学号为%d的学生已经存在。\n", newNode.ID);
                break;
            }
            temp = temp.next;
        }
    }

Delete:
Illustration:

Code :

 //删除一个节点。
    //自我删除
    public void DoubleDelete(int id) {
        if (head.next == null) {
            System.out.println("链表为空！");
            return;
        }
        DoubleNode temp = head.next;
        while (true) {
            if (temp == null) {
                System.out.printf("要删除的%d节点不存在\n", id);
                break;
            } else if (temp.ID == id) {
                //找到要删除节点
                // 此时temp 就代表将要被删除节点
                //temp.pre.next 指 当前要被删除节点 的前一位 的后一位
                // temp.next  指 当前要被删除节点的后一位
                temp.pre.next = temp.next;
                // （当前要被删除节点 的前一位 的后一位）指向 （当前要被删除节点的后一位）
                //这样就完成了 temp节点的删除操作
 
                // 如果是最后一个节点，就不需要执行下面这句话，否则出现空指针
                if (temp.next != null) {
                    temp.next.pre = temp.pre;
                }
                break;
            }
            temp = temp.next;
        }
    }

Modification:
Kankan: It is actually the same as deleting a singly linked list.

Code:

//修改链表节点
    public void DoubleUpdate(DoubleNode newNode) {
        if (head.next == null) {
            System.out.println("链表为空！");
            return;
        }
        DoubleNode temp = head.next;
        while (true) {
            if (temp == null) {
                break;
            } else if (temp.ID == newNode.ID) {
                //找到要修改的节点
                temp.name = newNode.name;
                temp.mark = newNode.mark;
                return;
            }
            temp = temp.next;
        }
        System.out.printf("要修改的%d节点不存在\n", newNode.ID);
    }

Doubly linked list example:

Use a doubly linked list to create a student information management system to complete the addition, deletion and modification of student information.

package Linkedlist;
 
//双向链表。
public class DoubleLinkedListDemo {
    public static void main(String agrs[]) {
        DoubleNode stu1 = new DoubleNode(6, "张三", 99);
        DoubleNode stu2 = new DoubleNode(2, "李四", 99);
        DoubleNode stu3 = new DoubleNode(3, "王五", 99);
        DoubleNode stu4 = new DoubleNode(5, "王二", 99);
        DoubleNode stu5 = new DoubleNode(4, "小红", 99);
        DoubleNode stu6 = new DoubleNode(1, "小明", 99);
        DoubleNode stu7 = new DoubleNode(1, "小明", 99);
 
        DoubleLinkedlist doubleLinkedlist = new DoubleLinkedlist();
 
       /* doubleLinkedlist.add(stu1);
        doubleLinkedlist.add(stu2);
        doubleLinkedlist.add(stu3);
        doubleLinkedlist.add(stu4);
        doubleLinkedlist.add(stu5);
        doubleLinkedlist.add(stu6);
        doubleLinkedlist.add(stu7);*/
 
        doubleLinkedlist.Sortadd(stu1);
        doubleLinkedlist.Sortadd(stu2);
        doubleLinkedlist.Sortadd(stu3);
        doubleLinkedlist.Sortadd(stu4);
        doubleLinkedlist.Sortadd(stu5);
        doubleLinkedlist.Sortadd(stu6);
        doubleLinkedlist.add(stu7);
 
        System.out.println("原链表展示！");
        doubleLinkedlist.ShowList();
        System.out.println();
 
        doubleLinkedlist.DoubleDelete(6);
        doubleLinkedlist.DoubleDelete(15);
        System.out.println("删除后链表展示！");
        doubleLinkedlist.ShowList();
        System.out.println();
 
 
        DoubleNode stu8 = new DoubleNode(1, "李思成", 100);
        DoubleNode stu9 = new DoubleNode(20, "李成", 100);
        doubleLinkedlist.DoubleUpdate(stu8);
        doubleLinkedlist.DoubleUpdate(stu9);
        System.out.println("修改后链表展示！");
        doubleLinkedlist.ShowList();
        System.out.println();
    }
}
 
class DoubleLinkedlist {
    private DoubleNode head = new DoubleNode(0, "", 0);
 
    public DoubleNode getHead() {
        return head;
    }
 
    //添加一个节点到最后
    public void add(DoubleNode newNode) {
        DoubleNode temp = head;
        while (true) {
            if (temp.next == null) {
                // 当temp.next 为空时，证明temp为最后一个元素。
                temp.next = newNode; //temp节点的下一位指向新节点
                newNode.pre = temp;//新节点的前一位指向temp
                //这两步构成双向链表
                break;
            }else if (temp.next.ID == newNode.ID) {
                //ID相同证明 已经存在该学生。
                System.out.printf("要插入学号为%d的学生已经存在。\n", newNode.ID);
                break;
            }
            temp = temp.next;
        }
    }
 
    //按学号顺序添加节点
    public void Sortadd(DoubleNode newNode) {
        DoubleNode temp = head;
        while (true) {
            if (temp.next == null) {
                //说明要添加的节点序号在当前链表中最大，因此直接添加在末尾。
                temp.next = newNode;//temp节点的下一位指向新节点
                newNode.pre = temp;//新节点的前一位指向temp
                //这两步构成双向链表
                break;
            } else if (temp.next.ID > newNode.ID) {
                //当前节点的下一位节点的编号大于 要添加的新节点，则证明新节点要添加在temp节点之后
                newNode.next = temp.next;//要添加节点的下一位 指向temp当前节点的下一位
                temp.next.pre = newNode;//temp当前节点的下一位的前一位 指向 新节点构成双向链表
                temp.next = newNode; // 再让当前节点的下一位指向 新节点
                newNode.pre = temp;//新节点的前一位 指向 当前节点temp
                //这样连接完成后就将  新节点插入 到 原本链表的temp节点与temp.next节点之间
                break;
            }else if (temp.next.ID == newNode.ID) {
                //ID相同证明 已经存在该学生。
                System.out.printf("要插入学号为%d的学生已经存在。\n", newNode.ID);
                break;
            }
            temp = temp.next;
        }
    }
 
    //删除一个节点。
    //自我删除
    public void DoubleDelete(int id) {
        if (head.next == null) {
            System.out.println("链表为空！");
            return;
        }
        DoubleNode temp = head.next;
        while (true) {
            if (temp == null) {
                System.out.printf("要删除的%d节点不存在\n", id);
                break;
            } else if (temp.ID == id) {
                //找到要删除节点
                // 此时temp 就代表将要被删除节点
                //temp.pre.next 指 当前要被删除节点 的前一位 的后一位
                // temp.next  指 当前要被删除节点的后一位
                temp.pre.next = temp.next;
                // （当前要被删除节点 的前一位 的后一位）指向 （当前要被删除节点的后一位）
                //这样就完成了 temp节点的删除操作
 
                // 如果是最后一个节点，就不需要执行下面这句话，否则出现空指针
                if (temp.next != null) {
                    temp.next.pre = temp.pre;
                }
                break;
            }
            temp = temp.next;
        }
    }
 
    //修改链表节点
    public void DoubleUpdate(DoubleNode newNode) {
        if (head.next == null) {
            System.out.println("链表为空！");
            return;
        }
        DoubleNode temp = head.next;
        while (true) {
            if (temp == null) {
                break;
            } else if (temp.ID == newNode.ID) {
                //找到要修改的节点
                temp.name = newNode.name;
                temp.mark = newNode.mark;
                return;
            }
            temp = temp.next;
        }
        System.out.printf("要修改的%d节点不存在\n", newNode.ID);
    }
 
    public void ShowList() {
        // 判断链表是否为空
        if (head.next == null) {
            System.out.println("链表为空");
            return;
        }
        // 因为头节点，不能动，因此我们需要一个辅助变量来遍历
        DoubleNode temp = head.next;
        while (true) {
            // 判断是否到链表最后
            if (temp == null) {
                break;
            }
            System.out.println(temp);// 输出节点的信息
            temp = temp.next;
        }
    }
}
 
class DoubleNode {
    public int ID; // 编号。
    public String name;
    public int mark;
    public DoubleNode next;
    public DoubleNode pre; // 前一个（Previous）
 
    public DoubleNode(int ID, String name, int mark) {
        this.ID = ID;
        this.name = name;
        this.mark = mark;
    }
 
    @Override
    public String toString() {
        return "DoubleNode{" + "ID=" + ID + ", name='" + name + '\'' + "mark=" + mark + '}';
    }
}

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