LinkedList类的实现

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本次简单介绍LinkedList泛型类的实现，为避免与类库中的类相混，将类名定义为MyLinkedList。下面概括需要实现的细节。

MyLinked类本身，它包含到两端的链、表的大小以及一些方法。
Node类，它可能是一个私有的嵌套类。一个节点包含数据以及到前一个节点的链和到后一个节点的链，还有一些适当的构造方法。
MyLinkedList将提供一个实现Iterator接口的类。这个类将存储迭代序列中的下一项的下标，并提供next、hasNext和remove等方法的实现。MyArrayList的迭代器方法直接返回实现的Iterator接口的该类的新构造的实例。

package com.zs.structures.list.linkedlist;import java.util.ConcurrentModificationException;import java.util.Iterator;import java.util.NoSuchElementException;/** * LinkedList类实现 * @author ZS * */public class MyLinkedList<AnyType> implements Iterable<AnyType>{    private int theSize;    private int modCount = 0;    private Node<AnyType> beginMarker;    private Node<AnyType> endMarker;    private static class Node<AnyType>    {        public Node(AnyType data, Node<AnyType> prev, Node<AnyType> next)         {            this.data = data;            this.prev = prev;            this.next = next;        }        private AnyType data;        private Node<AnyType> prev;        private Node<AnyType> next;    }    public MyLinkedList()     {        clear();    }    public void clear()    {        beginMarker = new Node<AnyType>(null, null, null);        endMarker = new Node<AnyType>(null, beginMarker, null);        beginMarker.next = endMarker;        theSize = 0;        modCount++;    }    public int size()    {        return theSize;    }    public boolean isEmpty()    {        return theSize == 0;    }    public boolean add(AnyType x)    {        add(theSize, x);        return true;    }    public boolean add(int index, AnyType x)    {        addBefore(getNode(index), x);        return true;    }    public AnyType get(int index)    {        return getNode(index).data;    }    public AnyType set(int index, AnyType x)    {        Node<AnyType> old = getNode(index);        AnyType oldVal = old.data;        old.data = x;        return oldVal;    }    public AnyType remove(int index)    {        return remove(getNode(index));    }    private void addBefore(Node<AnyType> p, AnyType x)    {        Node<AnyType> newNode = new Node<AnyType>(x, p.prev, p);        newNode.prev.next = newNode;        p.prev = newNode;        theSize++;        modCount++;    }    private AnyType remove(Node<AnyType> p)    {        p.next.prev = p.prev;        p.prev.next = p.next;        theSize--;        modCount++;        return p.data;    }    private Node<AnyType> getNode(int index)    {        if(index < 0 || index > theSize)        {            throw new ArrayIndexOutOfBoundsException();        }        Node<AnyType> node;        if(index < theSize / 2)        {            node = beginMarker.next;            for (int i = 0; i < index; i++)             {                node = node.next;            }        }        else        {            node = endMarker;            for (int i = theSize; i > index; i--)             {                node = node.prev;            }        }        return node;    }    @Override    public Iterator<AnyType> iterator()     {        return new LinkedListIterator();    }    private class LinkedListIterator implements Iterator<AnyType>    {        private int expectedModCount = modCount;        private Node<AnyType> current = beginMarker.next;        private boolean okToRemove = false;        @Override        public boolean hasNext()         {            return current != endMarker;        }        @Override        public AnyType next()         {            if(modCount != expectedModCount)            {                throw new ConcurrentModificationException();            }            if(!hasNext())            {                throw new NoSuchElementException();            }            AnyType nextItem = current.data;            current = current.next;            okToRemove = true;            return nextItem;        }        public void remove()        {            if(modCount != expectedModCount)            {                throw new ConcurrentModificationException();            }            if(okToRemove)            {                throw new IllegalStateException();            }            MyLinkedList.this.remove(current.prev);            okToRemove = false;            expectedModCount++;        }    }}

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