一個LRU算法的實現

LRU是Least Recently Used的縮寫，即最近最少使用頁面置換算法，是爲虛擬頁式存儲管理服務的。該算法的初衷是有內存管理而被提出來的，其目的是爲解決“如何節省利用容量不大的內存爲最多的進程提供資源”時如何減少過多的讓進程去讀取外存。
這裏以鏈表法來實現LRU:
一點介紹
操作系統爲每個進程維護一條鏈表，鏈表的每個結點記錄一張頁面的地址。調用一次頁面，則把該頁面的結點從鏈中取出，放到鏈尾；要裝入新頁，則把鏈頭的頁面調出，同時生成調入頁面的結點，放到鏈尾。
LRU算法的理論基礎是:局部性原理

/*
 *Created on 2008-7-24
 */
import java.io.Serializable;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Vector;

/**
 * @author anwx<a href="mailto:[email protected]">An Weixiao</a>
 * @version $Id$
 */
public class LRUTest {
    protected HashMap<Object, Serializable> cache;
    protected Vector<Object> cacheList;
    protected int capacity = 3;

    private int getCapacity(){
        return this.capacity;
    }

    private int getSize(){
        return cache.size();
    }
    public LRUTest(){
        this.cache = new HashMap<Object, Serializable>();
        this.cacheList = new Vector<Object>();
    }
    private void moveToTop(Object identifier) {
        cacheList.insertElementAt(identifier,0);
        if ( getSize() >= getCapacity() ) {
            String toBeDeleted = (String)cacheList.lastElement();
            cache.remove(toBeDeleted);
            int lastElement = cacheList.size();
            cacheList.remove(lastElement-1);
        }
    }
    public Object get(Object identifier) {
        if ( cache.containsKey(identifier) ) {
            moveToTop(identifier);
            Serializable co = (Serializable)cache.get(identifier);
            return co;
        }
        else {
            return null;
        }
    }

    public void put(Object identifier, Serializable value) { 
        if (  getSize() < getCapacity() ) {            
            if ( !cache.containsKey(identifier) ) {             
                cacheList.insertElementAt(identifier,0);
            }            
            cache.put(identifier,value);
        }
        else {
            cache.put(identifier,value);
            moveToTop(identifier);
        }
    }
    private void print(){
        System.out.println("data, key in cache");
        Object key = null;
        Serializable value = null;
        for(Iterator it = cache.keySet().iterator(); it.hasNext();){
            key = it.next();
            System.out.println(String.format("[%s, %s]", cache.get(key), key));
        }
        System.out.println("key info sequence");
        for(Object o: cacheList){
            System.out.println(o);
        }
    }
    public static void main(String args[]){
        LRUTest test = new LRUTest();
        test.put("1", "a");
        test.put("2", "b");
        test.put("3", "c");
        test.print();
        test.put("4", "d");
        test.put("5", "e");
        test.print();
    }
}