LinkedList

一. LinkedList简介

LinkedList和ArrayList一样, 在集合框架中, LInkedList也是一个类, 实现了List接口:

但是与我们上次定义的MySingleList不同, 上次的定义的无头单向非循环链表, 而LinkedLIst是无头双向非循环链表, 画图理解一下:

二.?LinkedList的简单实现

无头双向非循环链表的实现:

?IList.java:

public interface IList {
    //头插法
     void addFirst(int data);
    //尾插法
     void addLast(int data);
    //任意位置插入,第一个数据节点为0号下标
     void addIndex(int index,int data);
    //查找是否包含关键字key是否在单链表当中
     boolean contains(int key);
    //删除第一次出现关键字为key的节点
     void remove(int key);
    //删除所有值为key的节点
     void removeAllKey(int key);
    //得到单链表的长度
     int size();
     void clear() ;
     void display() ;

}

IndexException.java:

public class IndexException extends RuntimeException{
    public IndexException() {
    }

    public IndexException(String message) {
        super(message);
    }
}

?KeyException.java:

public class KeyException extends RuntimeException{
    public KeyException() {
    }

    public KeyException(String message) {
        super(message);
    }
}

MyLinkedList.java:

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Jiang Jinxi
 * Date: 2023-12-27
 * Time: 13:42
 */
public class MyLinkedList implements IList {
    static class ListNode{
        public ListNode prev;
        public int val;
        public  ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }
    public ListNode head;
    public ListNode last;

    @Override
    public void addFirst(int data) {
        ListNode node = new ListNode(data);
        if(head == null){
            head = node;
            last = node;
        }else{
            node.next = head;
            head.prev = node;
            head = node;

        }

    }

    @Override
    public void addLast(int data) {
        ListNode node = new ListNode(data);
        if(head == null){
            head = node;
            last = node;
        }else{
            last.next = node;
            node.prev = last;
            last = node;
        }


    }

    @Override
    public void addIndex(int index, int data) {
        if(index < 0 || index > size()){
            throw new IndexException("index 不合法" + index);
        }
        if(index == 0){
            addFirst(data);
            return;
        }
        if(index == size()){
            addLast(data);
            return;
        }
        ListNode cur = head;
        while(index != 0){
            cur = cur.next;
            index--;
        }

//插入结点
       ListNode node = new ListNode(data);
        node.next = cur;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;


    }

    @Override
    public boolean contains(int key) {
        ListNode cur = head;
        while(cur!=null) {
            if (cur.val == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    @Override
    public void remove(int key) {
        if(!contains(key)){
            throw new KeyException("找不到key" + key);
        }
//如果只有一个结点且该节点的值就是我要删的数字
       if(head.next == null && head.val == key){
            head = null;
            last = null;
            return;
        }
//循环遍历结点
        ListNode cur = head;
        while(cur!=null) {
            if (cur.val == key) {
//如果要删除的是头结点
                if(cur == head){
                    head = head.next;
                    head.prev = null;
                    return;
                }
//如果要删除的是尾结点
                if(cur == last){
                    last = last.prev;
                    last.next = null;
                    return;
                }
//是中间结点
                cur.prev.next = cur.next;
                cur.next.prev = cur.prev;
                return;

            }
            cur = cur.next;
        }

    }

    @Override
    public void removeAllKey(int key) {
        if(!contains(key)){
            throw new KeyException("找不到key" + key);
        }
        ListNode cur = head;
        if(cur.next == null && cur.val == key){
            head = null;
            last = null;
            return;
        }
        while(cur!=null) {
            if (cur.val == key) {
                if(cur == head){
                    head = head.next;
                    head.prev = null;
                }
                if(cur == last) {
                    last = last.prev;
                    last.next = null;
                }
                cur.prev.next = cur.next;
                cur.next.prev = cur.prev;
            }
            cur = cur.next;
        }

    }

    @Override
    public int size() {
        ListNode cur = head;
        int count = 0;
        while(cur != null){
            cur = cur.next;
            count++;
        }

        return count;
    }

    @Override
    public void clear() {
        head = null;
        last = null;

    }

    @Override
    public void display(){
        ListNode cur = head;
        while(cur != null) {
            System.out.println(cur.val + " ");
            cur = cur.next;//遍历所有节点
        }
    }
}

三. LinkedList的使用

1. LinkList的构造

1)无参构造

// 构造一个空的 LinkedList

List < Integer > list1 = new LinkedList <> ();

2)使用其他集合容器中元素构造List ?

List < String > list2 = new ArrayList <> ();

list2 . add ( "JavaSE" );

list2 . add ( "JavaWeb" );

list2 . add ( "JavaEE" );

// 使用 ArrayList 构造 LinkedList

List < String > list3 = new LinkedList <> ( list2 );

2. LinkedList的其他常用方法介绍?

方法与ArrayList类似, 不再赘述

3. LinkedList的遍历

第一种:for循环

// 使用下标+for遍历

for (int i = 0; i < linkedList.size(); i++) {

????????System.out.print(linkedList.get(i) + " ");

}

?第二种: for-each

// 借助foreach遍历

for (Integer x?: linkedList) {

????????System.out.print(x?+ " ");

}

System.out.println();

第三种: 使用迭代器

可以使用迭代器的原因是: 继承了Iterable接口

从前往后:?

Iterator<Integer> it = linkedList.iterator();

while(it.hasNext()){

????????System.out.print(it.next() + " ");

}

或

ListIterator<Integer> it = linkedList.listIterator();

while(it.hasNext()){

????????System.out.print(it.next() + " ");

}

注: ListIterator是Iterator的子类

?从后往前:

ListIterator<Integer> it = linkedList.listIterator(linkedList.size() );

while(it.hasPrevious()){

????????System.out.print(it.previous() + " ");

}

四. ArrayList和LinkedList的区别