页面置换算法java实现

以下是Java实现五种页面置换算法的示例代码：

1. Optimal算法

public class Optimal {
    public static void main(String[] args) {
        int[] pages = {1, 3, 0, 3, 5, 6};
        int[] frames = new int[3];
        int faults = 0;
        boolean full = false;
        int farthest = 0;
        int replace = 0;

        for (int i = 0; i < pages.length; i++) {
            int page = pages[i];
            int j;
            for (j = 0; j < frames.length; j++) {
                if (frames[j] == page) {
                    break;
                }
                if (frames[j] == 0) {
                    frames[j] = page;
                    faults++;
                    full = false;
                    break;
                }
                if (j == frames.length - 1) {
                    full = true;
                }
            }
            if (full) {
                int[] temp = new int[frames.length];
                boolean[] used = new boolean[frames.length];
                for (int k = i + 1; k < pages.length; k++) {
                    for (int l = 0; l < frames.length; l++) {
                        if (pages[k] == frames[l] && !used[l]) {
                            temp[l] = k;
                            used[l] = true;
                            break;
                        }
                        if (l == frames.length - 1) {
                            temp[l] = Integer.MAX_VALUE;
                        }
                    }
                }
                farthest = 0;
                replace = 0;
                for (int k = 0; k < temp.length; k++) {
                    if (temp[k] > farthest) {
                        farthest = temp[k];
                        replace = k;
                    }
                }
                frames[replace] = page;
                faults++;
            }
            System.out.print("Page " + page + ": ");
            for (int k = 0; k < frames.length; k++) {
                System.out.print(frames[k] + " ");
            }
            System.out.println();
        }
        System.out.println("Page faults: " + faults);
    }
}

2. FIFO算法

public class FIFO {
    public static void main(String[] args) {
        int[] pages = {1, 3, 0, 3, 5, 6};
        int[] frames = new int[3];
        int faults = 0;
        int pointer = 0;
        boolean full = false;

        for (int i = 0; i < pages.length; i++) {
            int page = pages[i];
            int j;
            for (j = 0; j < frames.length; j++) {
                if (frames[j] == page) {
                    break;
                }
                if (frames[j] == 0) {
                    frames[j] = page;
                    faults++;
                    full = false;
                    break;
                }
                if (j == frames.length - 1) {
                    full = true;
                }
            }
            if (full) {
                frames[pointer] = page;
                faults++;
                pointer++;
                if (pointer == frames.length) {
                    pointer = 0;
                }
            }
            System.out.print("Page " + page + ": ");
            for (int k = 0; k < frames.length; k++) {
                System.out.print(frames[k] + " ");
            }
            System.out.println();
        }
        System.out.println("Page faults: " + faults);
    }
}

3. LRU算法

public class LRU {
    public static void main(String[] args) {
        int[] pages = {1, 3, 0, 3, 5, 6};
        int[] frames = new int[3];
        int faults = 0;
        boolean full = false;
        int replace = 0;

        for (int i = 0; i < pages.length; i++) {
            int page = pages[i];
            int j;
            for (j = 0; j < frames.length; j++) {
                if (frames[j] == page) {
                    break;
                }
                if (frames[j] == 0) {
                    frames[j] = page;
                    faults++;
                    full = false;
                    break;
                }
                if (j == frames.length - 1) {
                    full = true;
                }
            }
            if (full) {
                int[] temp = new int[frames.length];
                boolean[] used = new boolean[frames.length];
                for (int k = i - 1; k >= 0; k--) {
                    for (int l = 0; l < frames.length; l++) {
                        if (pages[k] == frames[l] && !used[l]) {
                            temp[l] = k;
                            used[l] = true;
                            break;
                        }
                        if (l == frames.length - 1) {
                            temp[l] = Integer.MIN_VALUE;
                        }
                    }
                }
                replace = 0;
                int min = temp[0];
                for (int k = 1; k < temp.length; k++) {
                    if (temp[k] < min) {
                        min = temp[k];
                        replace = k;
                    }
                }
                frames[replace] = page;
                faults++;
            }
            System.out.print("Page " + page + ": ");
            for (int k = 0; k < frames.length; k++) {
                System.out.print(frames[k] + " ");
            }
            System.out.println();
        }
        System.out.println("Page faults: " + faults);
    }
}

4. LFU算法

public class LFU {
    public static void main(String[] args) {
        int[] pages = {1, 3, 0, 3, 5, 6};
        int[] frames = new int[3];
        int[] counts = new int[3];
        int faults = 0;
        boolean full = false;
        int replace = 0;

        for (int i = 0; i < pages.length; i++) {
            int page = pages[i];
            int j;
            for (j = 0; j < frames.length; j++) {
                if (frames[j] == page) {
                    counts[j]++;
                    break;
                }
                if (frames[j] == 0) {
                    frames[j] = page;
                    counts[j]++;
                    faults++;
                    full = false;
                    break;
                }
                if (j == frames.length - 1) {
                    full = true;
                }
            }
            if (full) {
                replace = 0;
                int min = counts[0];
                for (int k = 1; k < counts.length; k++) {
                    if (counts[k] < min) {
                        min = counts[k];
                        replace = k;
                    }
                }
                frames[replace] = page;
                counts[replace] = 1;
                faults++;
            }
            System.out.print("Page " + page + ": ");
            for (int k = 0; k < frames.length; k++) {
                System.out.print(frames[k] + " ");
            }
            System.out.println();
        }
        System.out.println("Page faults: " + faults);
    }
}

5. 改进型Clock算法

public class Clock {
    public static void main(String[] args) {
        int[] pages = {1, 3, 0, 3, 5, 6};
        int[] frames = new int[3];
        boolean[] ref_bits = new boolean[3];
        int faults = 0;
        int pointer = 0;

        for (int i = 0; i < pages.length; i++) {
            int page = pages[i];
            int j;
            for (j = 0; j < frames.length; j++) {
                if (frames[j] == page) {
                    ref_bits[j] = true;
                    break;
                }
                if (frames[j] == 0) {
                    frames[j] = page;
                    ref_bits[j] = true;
                    faults++;
                    break;
                }
            }
            if (j == frames.length) {
                while (ref_bits[pointer]) {
                    ref_bits[pointer] = false;
                    pointer++;
                    if (pointer == frames.length) {
                        pointer = 0;
                    }
                }
                frames[pointer] = page;
                ref_bits[pointer] = true;
                pointer++;
                if (pointer == frames.length) {
                    pointer = 0;
                }
                faults++;
            }
            System.out.print("Page " + page + ": ");
            for (int k = 0; k < frames.length; k++) {
                System.out.print(frames[k] + " ");
            }
            System.out.println();
        }
        System.out.println("Page faults: " + faults);
    }
}