LRUPageFrame.java

package cn.xl.basic.linklist;

/**
 * 用双向链表实现LRU(Least Recently Used 近期最少使用算法)
 * @author CoderXLoong
 *
 */
public class LRUPageFrame {

	private static class Node {

		Node prev;
		Node next;
		int pageNum;

		Node(Node _prev,int _pageNum,Node _next) {
			this.prev = _prev;
			this.pageNum = _pageNum;
			this.next = _next;
		}
	}

	private int capacity;
	private int size;

	private Node first;// 链表头
	private Node last;// 链表尾


	public LRUPageFrame(int capacity) {

		this.capacity = capacity;

	}

	/**
	 * 获取缓存中对象
	 * 
	 * @param key
	 * @return
	 */
	public void access(int pageNum) {

		if(first != null && first.pageNum == pageNum){
			return;
		}

		removeNode(pageNum);
		if(size()+1 > capacity){
			removeLast();
		}
		addFirst(pageNum);

	}



	private int size(){
		return size;
	}


	private void addFirst(int pageNum){
		final Node f = first;
		final Node newNode = new Node(null,pageNum,f);
		if(f == null){
			last = newNode;
		}else{
			f.prev = newNode;
		}
		first = newNode;
		size++;
	}


	private void removeLast(){

		final Node l = last;
		final Node prev = l.prev;
		prev.next = null;
		l.prev = null;
		last = prev;
		size --;
	}


	private void removeNode(int pageNum){
		Node node = first;
		while(node != null){
			if(node.pageNum == pageNum){
				if(node == last){
					removeLast();
				}else{
					final Node prev = node.prev; 
					final Node next = node.next;
					prev.next = next;
					next.prev = prev;
					node.prev = null;
					node.next = null;
					size--;
				}
				break;
			}else{
				node = node.next;
			}
		}


	}



	public String toString(){
		StringBuilder buffer = new StringBuilder();
		Node node = first;
		while(node != null){
			buffer.append(node.pageNum);			

			node = node.next;
			if(node != null){
				buffer.append(",");
			}
		}
		return buffer.toString();
	}

}