/**
* 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
* @return
*/
int size = 0;
public void access(int pageNum) {
if(size == 0){
Node node = new Node();
node.pageNum = pageNum;
node.prev = node.next = null;
first = last = node;
size++;
}else{
if(first.pageNum == pageNum){
return;
}
if(size == 1){
addToFirst(pageNum);
}else {
if (last.pageNum == pageNum) {
moveLastToFirst();
return;
}
Node iteratorNode = first;
while (iteratorNode.next != null && iteratorNode.pageNum != pageNum) {
iteratorNode = iteratorNode.next;
}
if (iteratorNode == last) {
addToFirst(pageNum);
if (size > capacity) {
last = last.prev;
last.next = null;
}
} else {
moveToFirst(iteratorNode);
}
}
}
}
private void moveLastToFirst() {
last.next = first;
first.prev = last;
first = last;
last = last.prev;
last.next = null;
first.prev = null;
}
private void moveToFirst(Node iteratorNode){
iteratorNode.prev.next = iteratorNode.next;
iteratorNode.next.prev = iteratorNode.prev;
iteratorNode.prev = null;
iteratorNode.next = first;
first.prev = iteratorNode;
first = iteratorNode;
}
private void addToFirst(int pageNum) {
Node node = new Node();
node.pageNum = pageNum;
node.prev = null;
node.next = first;
first.prev = node;
first = node;
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();
}
}