package io.github.vxzh.lru;
/**
* 用双向链表实现LRU算法
*/
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 pageNum
* @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) {
Node f = first;
Node newNode = new Node(null, pageNum, f);
if (f == null)
last = newNode;
else
f.prev = newNode;
first = newNode;
size++;
}
private void removeLast() {
Node l = last;
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();
}
}