java生成一个页面置换算法实验

以下是 Java 实现的页面置换算法实验代码：

import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.Queue;

public class PageReplacementExperiment {

    public static void main(String[] args) {
        // 页面访问顺序
        int[] pageList = {3, 4, 2, 8, 1, 2, 3, 3, 4, 2, 3, 4, 6, 1, 5, 4, 2, 3, 7, 8, 4, 8, 7, 3, 4, 7, 8, 5, 4, 5, 3, 4, 3, 7, 8, 4, 5, 1, 2, 1};
        // 内存块数
        int numMemoryBlocks = 4;

        // 执行 OPT 算法
        int[] optFaultSequence = opt(pageList, numMemoryBlocks);
        double optPageFaultRate = getPageFaultRate(optFaultSequence, pageList.length);
        System.out.println("OPT 算法：");
        System.out.println("缺页率：" + optPageFaultRate);
        System.out.println("缺页序列：" + Arrays.toString(optFaultSequence));

        // 执行 FIFO 算法
        int[] fifoFaultSequence = fifo(pageList, numMemoryBlocks);
        double fifoPageFaultRate = getPageFaultRate(fifoFaultSequence, pageList.length);
        System.out.println("FIFO 算法：");
        System.out.println("缺页率：" + fifoPageFaultRate);
        System.out.println("缺页序列：" + Arrays.toString(fifoFaultSequence));

        // 执行 LRU 算法
        int[] lruFaultSequence = lru(pageList, numMemoryBlocks);
        double lruPageFaultRate = getPageFaultRate(lruFaultSequence, pageList.length);
        System.out.println("LRU 算法：");
        System.out.println("缺页率：" + lruPageFaultRate);
        System.out.println("缺页序列：" + Arrays.toString(lruFaultSequence));
    }

    /**
     * OPT 算法
     */
    public static int[] opt(int[] pageList, int numMemoryBlocks) {
        int[] faultSequence = new int[pageList.length];
        int[] memoryBlocks = new int[numMemoryBlocks];
        ArrayList<Integer> pageListRemaining = new ArrayList<>();
        for (int i = 0; i < pageList.length; i++) {
            pageListRemaining.add(pageList[i]);
        }

        for (int i = 0; i < pageList.length; i++) {
            int page = pageList[i];
            boolean pageInMemory = false;

            // 判断页面是否在内存块数组中
            for (int j = 0; j < numMemoryBlocks; j++) {
                if (memoryBlocks[j] == page) {
                    pageInMemory = true;
                    break;
                }
            }

            if (!pageInMemory) {
                // 如果页面不在内存块数组中，则进行页面置换
                faultSequence[i] = page;
                int[] memoryBlocksNext = new int[numMemoryBlocks];
                for (int j = 0; j < numMemoryBlocks; j++) {
                    // 如果内存块未被使用，则直接将页面加入内存块
                    if (memoryBlocks[j] == 0) {
                        memoryBlocksNext[j] = page;
                        break;
                    } else {
                        // 如果内存块已被使用，则查找下一次使用该页面的位置
                        boolean pageFound = false;
                        for (int k = i + 1; k < pageList.length; k++) {
                            if (memoryBlocks[j] == pageList[k]) {
                                memoryBlocksNext[j] = memoryBlocks[j];
                                pageFound = true;
                                break;
                            }
                        }
                        if (!pageFound) {
                            memoryBlocksNext[j] = page;
                            break;
                        }
                    }
                }
                memoryBlocks = memoryBlocksNext;
            }
        }

        return faultSequence;
    }

    /**
     * FIFO 算法
     */
    public static int[] fifo(int[] pageList, int numMemoryBlocks) {
        int[] faultSequence = new int[pageList.length];
        int[] memoryBlocks = new int[numMemoryBlocks];
        Queue<Integer> fifoQueue = new LinkedList<>();

        for (int i = 0; i < pageList.length; i++) {
            int page = pageList[i];
            boolean pageInMemory = false;

            // 判断页面是否在内存块数组中
            for (int j = 0; j < numMemoryBlocks; j++) {
                if (memoryBlocks[j] == page) {
                    pageInMemory = true;
                    break;
                }
            }

            if (!pageInMemory) {
                // 如果页面不在内存块数组中，则进行页面置换
                faultSequence[i] = page;
                int memoryBlockIndex = -1;
                for (int j = 0; j < numMemoryBlocks; j++) {
                    // 如果内存块未被使用，则直接将页面加入内存块
                    if (memoryBlocks[j] == 0) {
                        memoryBlockIndex = j;
                        break;
                    } else {
                        // 如果内存块已被使用，则查找 FIFO 队列中的页面
                        if (fifoQueue.peek() == memoryBlocks[j]) {
                            memoryBlockIndex = j;
                            break;
                        }
                    }
                }
                fifoQueue.add(page);
                if (memoryBlockIndex != -1) {
                    memoryBlocks[memoryBlockIndex] = page;
                    fifoQueue.poll();
                }
            }
        }

        return faultSequence;
    }

    /**
     * LRU 算法
     */
    public static int[] lru(int[] pageList, int numMemoryBlocks) {
        int[] faultSequence = new int[pageList.length];
        int[] memoryBlocks = new int[numMemoryBlocks];
        ArrayList<Integer> pageListRemaining = new ArrayList<>();
        for (int i = 0; i < pageList.length; i++) {
            pageListRemaining.add(pageList[i]);
        }

        for (int i = 0; i < pageList.length; i++) {
            int page = pageList[i];
            boolean pageInMemory = false;

            // 判断页面是否在内存块数组中
            for (int j = 0; j < numMemoryBlocks; j++) {
                if (memoryBlocks[j] == page) {
                    pageInMemory = true;
                    break;
                }
            }

            if (!pageInMemory) {
                // 如果页面不在内存块数组中，则进行页面置换
                faultSequence[i] = page;
                int[] memoryBlocksNext = new int[numMemoryBlocks];
                int[] pageLastUsed = new int[numMemoryBlocks];
                for (int j = 0; j < numMemoryBlocks; j++) {
                    // 如果内存块未被使用，则直接将页面加入内存块
                    if (memoryBlocks[j] == 0) {
                        memoryBlocksNext[j] = page;
                        pageLastUsed[j] = i;
                        break;
                    } else {
                        // 如果内存块已被使用，则查找最近最久未使用的页面
                        int lruIndex = -1;
                        int lruTime = Integer.MAX_VALUE;
                        for (int k = 0; k < numMemoryBlocks; k++) {
                            int timeSinceLastUse = i - pageLastUsed[k];
                            if (timeSinceLastUse > 0 && timeSinceLastUse < lruTime) {
                                lruIndex = k;
                                lruTime = timeSinceLastUse;
                            }
                        }
                        if (lruIndex != -1) {
                            memoryBlocksNext[lruIndex] = page;
                            pageLastUsed[lruIndex] = i;
                            break;
                        }
                    }
                }
                memoryBlocks = memoryBlocksNext;
            } else {
                // 如果页面已经在内存块数组中，则更新该页面的最近使用时间
                for (int j = 0; j < numMemoryBlocks; j++) {
                    if (memoryBlocks[j] == page) {
                        pageLastUsed[j] = i;
                        break;
                    }
                }
            }
        }

        return faultSequence;
    }

    /**
     * 计算缺页率
     */
    public static double getPageFaultRate(int[] faultSequence, int numPages) {
        int numFaults = 0;
        for (int i = 0; i < faultSequence.length; i++) {
            if (faultSequence[i] != 0) {
                numFaults++;
            }
        }
        return (double) numFaults / numPages;
    }

}

以上代码中实现了三种页面置换算法：OPT、FIFO 和 LRU。在 `main` 方法中调用这三个方法，并计算缺页率和缺页序列。