45 容器（四）——手写LinkedList

概念

LinkedList级双向链表，它的单位是节点，每一个节点都要一个头指针和一个尾指针，称为前驱和后继。第一个节点的头指针指向最后一个节点，最后一个节点的尾指针指向第一个节点，形成环路。

链表增删速度快，查询速度慢。

手写LinkedList

通过今天手写LinkedList，我觉得，我并没有体验到链表比ArrayList快，以后再来深究。

先写一个MyLinkedList类

package _20191210;

import java.util.NoSuchElementException;

public class MyLinkedList {
	//List myLikedList = new LinkedList();
	Node first;
	Node last;
	transient int size = 0;
	public MyLinkedList(){
		
	}
	
	//linkFirst 插为第一个节点
	private void linkFirst(E e) {
		final Node f = first;
		final Node newNode = new Node(null,e,f);
		first = newNode;
		if(f == null)
			last = newNode;
		else
			f.prev = newNode;
		size++;
		//	modSize++;
	}
	
	//linkLast 插为最后一个节点
	private void linkLast(E e) {
		final Node l = last;
		final Node newNode = new Node(last,e,null);
		last = newNode;//将它作为最后一个节点last
		if(l == null)//当插入的是列表中的第一个节点时，将该节点设为last与first
			first = newNode;
		else
			l.next = newNode;
		size++;
//      modCount++;
	}
	//addFirst 添加到列表的第一个
	public void addFirst(E e) {
		linkFirst(e);
	}
	//addLast
	public void addLast(E e) {
		linkLast(e);
	}
	//add
	public void add(E e) {
		linkLast(e);
		
	}
	/**
	 * returns the first element in this List
	 */
	public E getFirst() {
		final Node f = first;
		if(f == null) {
			throw new NoSuchElementException();
		}
		return f.item;
	}
	//getLast返回最后一个元素
	public E getLast() {
		final Node l = last;
		if(last == null) {
			throw new NoSuchElementException();
		}
		return l.item;
	}
	/**
	 * removes and returns the first element from the link list.
	 */
	public E removeFirst(){
		final Node f = first;
		final Node next = first.next;
		if(f == null) {
			throw new NoSuchElementException();
		}
		first = next;
		first.prev = null;
		size--;
		return f.item;
	}
	/**
	 * removes and returns the last element from link list
	 */
	public E removeLast() {
		final Node l = last;
		if(l == null) {
			throw new NoSuchElementException();
		}
		if(last.prev == null) {
			E e = last.item;
			last = null;
			first = null;
			size--;
			return e;
		}
		final Node prev = last.prev;
		last = prev;
		size--;
		return l.item;
	}
	/**
	 * returns the size of this list
	 */
	public int size() {
		return size;
	}
	/**
	 * remove the first occurrence of the specified element form this list,if it is
	 * present.
	 */
	public boolean remove(Object o) {
		Node tmp = first;
		while(tmp!=null) {
			if(tmp.item == o) {
				Node prev = tmp.prev;
				Node next = tmp.next;
				prev.next = next;
				next.prev = prev;
				size--;
				return true;
			}
			tmp = tmp.next;
		}
		return false;
	}
	/**
	 * returns the index of the first occurrence of the specified element in this list
	 * or -1 if this list does not contain the element
	 */
	public int indexOf(Object o) {
		int index = 0;
		if(null == o) {
			for(Node f = first;f != null;f = f.next) {
				if(f.item==o) {
					return index;
				}
				index++;
			}
		}else {
			for(Node f = first;f != null;f = f.next) {
				if(o.equals(f.item)) {
					return index;
				}
				index++;
			}
		}
		return -1;
	}
	//toString
	public String toString() {
		StringBuffer sb = new StringBuffer();
		sb.append("[");
		Node tmp = null;
		tmp = first;
		do{
				if(tmp==null) break;
				sb.append(tmp.item);
				if(tmp.next!=null) sb.append(", ");
				tmp = tmp.next;
			
		}while(tmp!=null);
		sb.append("]");
		return sb.toString();
	}
	
	//内部类：节点
	private static class Node{
		E item;//本体
		Node next;//后继
		Node prev;//前驱
		public Node(Node prev,E element,Node next) {
			this.item = element;
			this.next = next;
			this.prev = prev;
		}
	}
}

　　

再写一个MyLinkedListTest测试类，测试手写LinkedList与官方LinkedList的运行结果。

package _20191210;

import java.util.LinkedList;
import java.util.List;

public class MyLinkedListTest {
	public static void main(String[] args) {
		System.out.println("---------自己写的LinkedList-----------");
		MyLinkedList mk = new MyLinkedList<>();
		mk.add("Y");
		mk.add("E");
		mk.add("S");
		System.out.println(mk);
		System.out.println(mk.size());
		System.out.println("移除E:"+mk.remove("E"));
		System.out.println(mk);
		System.out.println(mk.getFirst());
		System.out.println(mk.getLast());
		System.out.println("S的位置为："+mk.indexOf("S"));
		System.out.println("removeFirst:"+mk.removeFirst());
		System.out.println(mk.size());
		System.out.println(mk);
		System.out.println("removeLast:"+mk.removeLast());
		System.out.println(mk);
		System.out.println("---------官方LinkedList-------------");
		LinkedList linkList = new LinkedList<>();
		linkList.add("Y");
		linkList.add("E");
		linkList.add("S");
		System.out.println(linkList);
		System.out.println(linkList.size());
		System.out.println("移除E:"+linkList.remove("E"));
		System.out.println(linkList);
		System.out.println(linkList.getFirst());
		System.out.println(linkList.getLast());
		System.out.println("S的位置为："+linkList.indexOf("S"));
		System.out.println("removeFirst:"+linkList.removeFirst());
		System.out.println(linkList.size());
		System.out.println(linkList);
		System.out.println("removeLast:"+linkList.removeLast());
		System.out.println(linkList);
		
	}
}