在實現LinkedList的時候主要考慮三個類:
1.MyLinkedList類本身,它包含了兩端的鏈、標的大小以及一些方法,在鏈的兩端加了兩個額外的節點,頭結點(header node)和尾節點(tail node)用來標示鏈頭和鏈尾。
2.Node類,它可能是一個私有的嵌套類。一個節點包含數據以及前一個節點的連接和道下一個節點的連接,還有一個構造方法。
3.LinkedListIterator類,該類抽象了位置的概念,是一個私有類,並實現接口Iterator。提供了hasNext()、next()和remove()方法。
具體的看下面的代碼:
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* @author QuLei
*
* @param <AnyType>泛型表示任意的類型均可以放入容器內
* 自己實現LinkedList
*/
public class MyLinkedList<AnyType> implements Iterable<AnyType> {
private int theSize;
private int modCount;
//創建兩個額外的節點一個作爲頭結點,一個作爲尾節點
private Node<AnyType> beginMarker;
private Node<AnyType> endMarker;
/**
* @author QuLei
*
* @param <AnyType>
* 定義一個節點,表示鏈表的存儲結構
*/
private static class Node<AnyType>{
public AnyType data;
public Node<AnyType> prev;
public Node<AnyType> next;
public Node(AnyType data, Node<AnyType> prev, Node<AnyType> next) {
super();
this.data = data;
this.prev = prev;
this.next = next;
}
}
public MyLinkedList() {
clear();
}
/**
* change the size of the collection to zero
*/
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 size() == 0;
}
/**調用此方法就是直接在尾部添加
* @param x 要添加的元素
* @return 成功返回true,若失敗會拋異常出去
*/
public boolean add(AnyType x) {
add(size(),x);
return true;
}
/**
* @param idx
* @param x
*/
public void add(int idx,AnyType x) {
addBefore(getNode(idx),x);
}
/**修改指定位置的值
* @param idx
* @param newVal
* @return
*/
public AnyType set(int idx,AnyType newVal) {
Node<AnyType> p = getNode(idx);
AnyType oldVal = p.data;
p.data = newVal;
return oldVal;
}
/**刪除指定位置的元素
* @param idx
* @return
*/
public AnyType remove(int idx) {
return remove(getNode(idx));
}
/**查詢指定位置的值
* @param idx
* @return
*/
public AnyType get(int idx) {
return getNode(idx).data;
}
/**判斷是否包含某個元素
* @param x 要判斷的元素
* @return 返回是否包含該元素
*/
public boolean contains(AnyType x) {
Node<AnyType> p = beginMarker.next;
while(p != endMarker && !(p.data.equals(x))) {
p = p.next;
}
return (p != endMarker);
}
/**在給定節點前面插入元素
* @param p
* @param x
*/
private void addBefore(Node<AnyType> p,AnyType x) {
Node<AnyType> newNode = new Node<AnyType>(x, p.prev, p);
//newNode.prev = p.prev; 這兩句代碼可以直接放入構造器中
//newNode.next = p;
p.prev = p.prev.next = newNode; //把原來鏈中的結構鏈接上
theSize ++;
modCount ++;
}
private AnyType remove(Node<AnyType> p) {
p.prev.next = p.next;
p.next.prev = p.prev;
theSize --;
modCount ++;
return p.data;
}
/**獲取指定位置的節點
* @param idx :指定的位置
* @return :返回該指定位置處的節點
*/
private Node<AnyType> getNode(int idx){
Node<AnyType> p;
if(idx < 0 || idx > size()) {
throw new IndexOutOfBoundsException();
}
if(idx < size()/2) {
p = beginMarker;
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;
}
@Override
public Iterator<AnyType> iterator() {
// TODO Auto-generated method stub
return new LinkedListIterator();
}
private class LinkedListIterator implements Iterator<AnyType>{
//起始位置爲第一個節點
private Node<AnyType> current = beginMarker.next;
private int exceptedModCount = modCount;
private boolean okToRemove = false;
@Override
public boolean hasNext() {
// TODO Auto-generated method stub
return current != endMarker;
}
@Override
public AnyType next() {
// TODO Auto-generated method stub
if(modCount != exceptedModCount) {
throw new ConcurrentModificationException();
}
if(!hasNext()) {
throw new NoSuchElementException();
}
AnyType nextItem = current.data;
current = current.next;
okToRemove = true;
return nextItem;
}
public void remove() {
if(modCount != exceptedModCount) {
throw new ConcurrentModificationException();
}
if(!okToRemove) {
throw new IllegalStateException();
}
MyLinkedList.this.remove(current.prev);
okToRemove = false;
exceptedModCount ++;
}
}
}