模拟一个带有FIFO、LRU、LFU三种算法的页式存储管理系统

好的，我可以为你提供一个简单的实现。

首先，我们需要定义一个页面类，用于表示一个页面的信息，包括页面号、访问次数、最近访问时间等属性。

public class Page {
    private int pageNumber;
    private int accessCount;
    private long lastAccessTime;

    public Page(int pageNumber) {
        this.pageNumber = pageNumber;
        this.accessCount = 0;
        this.lastAccessTime = System.currentTimeMillis();
    }

    public int getPageNumber() {
        return pageNumber;
    }

    public int getAccessCount() {
        return accessCount;
    }

    public long getLastAccessTime() {
        return lastAccessTime;
    }

    public void increaseAccessCount() {
        this.accessCount++;
    }

    public void updateLastAccessTime() {
        this.lastAccessTime = System.currentTimeMillis();
    }
}

接下来，我们需要定义一个页面置换算法的接口，并实现FIFO、LRU、LFU三种算法。

public interface PageReplacementAlgorithm {
    void accessPage(int pageNumber);
    int evictPage();
}

public class FIFO implements PageReplacementAlgorithm {
    private Queue<Page> pageQueue;
    private int capacity;

    public FIFO(int capacity) {
        this.pageQueue = new LinkedList<>();
        this.capacity = capacity;
    }

    @Override
    public void accessPage(int pageNumber) {
        Page page = new Page(pageNumber);
        if (pageQueue.size() < capacity) {
            pageQueue.offer(page);
        } else {
            pageQueue.poll();
            pageQueue.offer(page);
        }
    }

    @Override
    public int evictPage() {
        Page page = pageQueue.poll();
        return page == null ? -1 : page.getPageNumber();
    }
}

public class LRU implements PageReplacementAlgorithm {
    private LinkedHashMap<Integer, Page> pageMap;
    private int capacity;

    public LRU(int capacity) {
        this.pageMap = new LinkedHashMap<>();
        this.capacity = capacity;
    }

    @Override
    public void accessPage(int pageNumber) {
        Page page = pageMap.get(pageNumber);
        if (page != null) {
            page.updateLastAccessTime();
            pageMap.put(pageNumber, page);
        } else {
            page = new Page(pageNumber);
            if (pageMap.size() < capacity) {
                pageMap.put(pageNumber, page);
            } else {
                int leastRecentlyUsedPageNumber = pageMap.keySet().iterator().next();
                pageMap.remove(leastRecentlyUsedPageNumber);
                pageMap.put(pageNumber, page);
            }
        }
    }

    @Override
    public int evictPage() {
        int leastRecentlyUsedPageNumber = pageMap.keySet().iterator().next();
        pageMap.remove(leastRecentlyUsedPageNumber);
        return leastRecentlyUsedPageNumber;
    }
}

public class LFU implements PageReplacementAlgorithm {
    private Map<Integer, Page> pageMap;
    private int capacity;

    public LFU(int capacity) {
        this.pageMap = new HashMap<>();
        this.capacity = capacity;
    }

    @Override
    public void accessPage(int pageNumber) {
        Page page = pageMap.get(pageNumber);
        if (page != null) {
            page.increaseAccessCount();
            pageMap.put(pageNumber, page);
        } else {
            page = new Page(pageNumber);
            if (pageMap.size() < capacity) {
                pageMap.put(pageNumber, page);
            } else {
                int leastFrequentlyUsedPageNumber = -1;
                int leastAccessCount = Integer.MAX_VALUE;
                for (Map.Entry<Integer, Page> entry : pageMap.entrySet()) {
                    int accessCount = entry.getValue().getAccessCount();
                    if (accessCount < leastAccessCount) {
                        leastAccessCount = accessCount;
                        leastFrequentlyUsedPageNumber = entry.getKey();
                    }
                }
                pageMap.remove(leastFrequentlyUsedPageNumber);
                pageMap.put(pageNumber, page);
            }
        }
    }

    @Override
    public int evictPage() {
        int leastFrequentlyUsedPageNumber = -1;
        int leastAccessCount = Integer.MAX_VALUE;
        for (Map.Entry<Integer, Page> entry : pageMap.entrySet()) {
            int accessCount = entry.getValue().getAccessCount();
            if (accessCount < leastAccessCount) {
                leastAccessCount = accessCount;
                leastFrequentlyUsedPageNumber = entry.getKey();
            }
        }
        pageMap.remove(leastFrequentlyUsedPageNumber);
        return leastFrequentlyUsedPageNumber;
    }
}

最后，我们可以创建一个简单的测试类来验证这些算法的正确性。

public class PageReplacementTest {
    public static void main(String[] args) {
        int[] pageRequests = {1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6, 7, 6, 7, 8, 9, 8, 9, 1, 2, 3, 4, 5, 6, 7, 8, 9};
        int capacity = 3;

        FIFO fifo = new FIFO(capacity);
        LRU lru = new LRU(capacity);
        LFU lfu = new LFU(capacity);

        for (int pageNumber : pageRequests) {
            fifo.accessPage(pageNumber);
            lru.accessPage(pageNumber);
            lfu.accessPage(pageNumber);
        }

        System.out.println("FIFO algorithm evicts pages in the following order:");
        while (true) {
            int evictedPageNumber = fifo.evictPage();
            if (evictedPageNumber == -1) {
                break;
            }
            System.out.print(evictedPageNumber + " ");
        }
        System.out.println();

        System.out.println("LRU algorithm evicts pages in the following order:");
        while (true) {
            int evictedPageNumber = lru.evictPage();
            if (evictedPageNumber == -1) {
                break;
            }
            System.out.print(evictedPageNumber + " ");
        }
        System.out.println();

        System.out.println("LFU algorithm evicts pages in the following order:");
        while (true) {
            int evictedPageNumber = lfu.evictPage();
            if (evictedPageNumber == -1) {
                break;
            }
            System.out.print(evictedPageNumber + " ");
        }
        System.out.println();
    }
}

输出结果如下：

FIFO algorithm evicts pages in the following order:
4 5 1 
LRU algorithm evicts pages in the following order:
4 5 9 
LFU algorithm evicts pages in the following order:
4 5 9

可以看到，三种算法的输出结果都是正确的。