package LRU;
/**
* 使用双向链表实现LRU算法
* @author 12946
*
*/
public class LRUPageFrame {
private static class Node {
Node prev = null;
Node next = null;
int pageNum;
Node(Object data) {
if(data != null){
this.pageNum = (Integer)data;
}
}
}
private int capacity;//链表总元素个数
private int currentSize;//链表当前元素个数
private Node first;// 链表头
private Node last;// 链表尾
public LRUPageFrame(int capacity) {
first = new Node(null);//栈底，元素最先放入的地方
last = new Node(null);//栈顶
this.currentSize = 0;
this.capacity = capacity;
}
/**
* 获取缓存中对象
*
* @param key
* @return
*/
public void access(int pageNum) {
Node newNode = new Node(pageNum);
if(currentSize == capacity){
Node tempNode = null;
if(getIndex(pageNum) == -1){//不包含
tempNode = first.next;
}else{//包含
tempNode = getNode(pageNum);
}
(tempNode.prev).next = tempNode.next;
(tempNode.next).prev = tempNode.prev;
newNode.next = last;
newNode.prev = last.prev;
last.prev = newNode;
newNode.prev.next = newNode;
}
if(currentSize < capacity){
Node point = first;
for(int i = 0; i < currentSize; i++){
point = point.next;
}
point.next = newNode;
newNode.prev = point;
newNode.next = last;
last.prev = newNode;
currentSize += 1;
}
}
public Node getNode(int data){
Node point = first.next;
for(int i = 0; i < capacity; i++){
if(point.pageNum == data){
return point;
}
point = point.next;
}
return null;
}
public int getIndex(int data){
Node point = first.next;
for(int i = 0; i < capacity; i++){
if(point.pageNum == data){
return i;
}
point = point.next;
}
return -1;
}
// 原toString
// 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();
// }
public String toString(){
StringBuilder sb = new StringBuilder();
Node point = last.prev;
while(point != first){
sb.append(point.pageNum);
if(point.prev != first){
sb.append(",");
}
point = point.prev;
}
return sb.toString();
}
}