package com.coding.basic;
/**
* 用双向链表实现LRU算法
* @author liuxin
*
*/
public class LRUPageFrame {
private static class Node {
Node prev;
Node next;
int pageNum;
Node() {
}
}
private int capacity;
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) {
Node node = findPageNumNode(pageNum);
if(node==null){
if(size()>=capacity){
removeLast();
}
push(pageNum);
}else{
moveToFirst(node);
}
}
public Node findPageNumNode(int pageNum) {
Node node = first;
while(node!=null){
if(node.pageNum==pageNum){
break;
}else{
node = node.next;
}
}
return node;
}
public void moveToFirst(Node node) {
if(first==null||node==null||first.pageNum==node.pageNum){
return;
}
if(node.pageNum == last.pageNum){
node.prev.next = null;
last = node.prev;
}else{
Node tPrev = node.prev;
Node tNext = node.next;
tPrev.next = tNext;
tNext.prev = tPrev;
}
node.prev = null;
node.next = first;
first = node;
}
public void push(int pageNum) {
if(size()==0){
first = new Node();
first.pageNum = pageNum;
last = first;
return ;
}
Node node;
node = new Node();
node.pageNum = pageNum;
node.next = first;
first.prev = node;
first = node;
}
public void removeLast() {
if(last==null){
return ;
}
if(size()==1){
first = null;
last = null;
return ;
}
Node temp = last.prev;
last.prev = null;
last = temp;
last.next = null;
}
public int size() {
int size = 0;
Node temp = first;
while (temp!=null) {
size++;
temp = temp.next;
}
return size;
}
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();
}
}