[置顶] 小伙伴们来自己实现LinkedList

继前面实现ArrayList后，今天和小伙伴一起实现LinkedList，LinkedList实现我们采用双向链表来实现，在每次查找时候，如果该查找元素位于该链表的前半段，则从开始检索，如果位于链表的后半段，则从尾部开始检索。以下先贴出代码：

package com.david.duan;

import java.util.Iterator;

public class MyLinkedList implements Iterable<Student>{
	//表示该链表的长度
	private int theSize;
	//每次链表被修改就增加此值
	private int modCount;
	//链表的头元素
	private Node<Student> beginMarker;
	//链表的尾元素
	private Node<Student> endMarker;
	//使用内部类来实现链表的每一个节点，每个节点有一个指向下一个元素的next，指向上一个元素的prev，以及自身的data
	private static class Node<Student> {
		public Node(Student data, Node<Student> prev, Node<Student> next) {
			this.data = data;
			this.prev = prev;
			this.next = next;
		}
		public Student data;
		public Node<Student> prev;
		public Node<Student> next;
	}
	//链表的构造方法
	public MyLinkedList () {
		clear();
	}
	//清除链表，即使得链表的头元素指向链表的尾元素
	public void clear () {
		beginMarker = new Node<Student>(null, null, null);
		endMarker = new Node<Student>(null, beginMarker, null);
		beginMarker.next = endMarker;
	}
	//返回链表的长度
	public int size() {
		return theSize;
	}
	//判断链表是否为空
	public boolean isEmplty() {
		return size() == 0;
	}
	//向链表中添加元素
	public boolean add(Student x) {
		add(size(), x);
		return true;
	}

	public void add(int idx, Student x) {
		addBefore(getNode(idx), x);
	}
	//获取该节点的data
	public Student get(int idx) {
		return getNode(idx).data;
	}
	//设置该节点的值
	public Student set(int idx, Student newData) {
		Node<Student> oldNode = getNode(idx);
		Student oldData = oldNode.data;
		oldNode.data = newData;
		return oldData;
	}
	//删除该节点，并返回该节点的值
	public Student remove(int idx) {
		return remove(getNode(idx));
	}

	private Student remove(Node<Student> p) {
		p.prev.next = p.next;
		p.next.prev = p.prev;
		theSize--;
		modCount++;
		return p.data;
	}
	//执行添加
	private void addBefore (Node<Student> p, Student x) {
		Node<Student> newNode = new Node<Student>(x, p.prev, p);
		newNode.prev.next = newNode;
		p.prev = newNode;
		modCount++;
	}
	//查找节点
	private Node<Student> getNode(int idx) {
		Node<Student> p;

		if(idx <0 || idx > size()) {
			throw new IndexOutOfBoundsException();
		}

		if(idx < size()/2) {
			p = beginMarker.next;
			for (int i = 0;i < idx;i++) {
				p = p.next;
			}
		}else {
			p = endMarker;
			for (int i = size();i>idx;i--) {
				p = p.prev;
			}
		}
		return p;
	}
	//此处类似于前面的ArrayList，用以保存并返回当前元素
	@Override
	public Iterator<Student> iterator() {
		return new LinkedListIterator();
	}

	private class LinkedListIterator implements java.util.Iterator<Student> {

		private Node<Student> current = beginMarker.next;
		private int expectedModCount = modCount;
		private boolean okToRemove = false;
		@Override
		public boolean hasNext() {
			return current != endMarker;
		}

		@Override
		public Student next() {
			if (modCount != expectedModCount ) {
				throw new java.util.ConcurrentModificationException();
			}
			if(!hasNext()) {
				throw new java.util.NoSuchElementException();
			}
			Student nextData = current.data;
			current = current.next;
			okToRemove = true;
			return nextData;
		}

		@Override
		public void remove() {
			if (modCount != expectedModCount ) {
				throw new java.util.ConcurrentModificationException();
			}
			if(!hasNext()) {
				throw new java.util.NoSuchElementException();
			}
			MyLinkedList.this.remove(current.prev);
			okToRemove = false;
			expectedModCount++;
		}

	}
}

此处讲解不太详细的地方，欢迎大家留言探讨。