用Java实现银行家算法

银行家算法是一种避免死锁的算法，它通过动态地分配资源来避免进程死锁。下面是Java实现银行家算法的步骤：

1.定义资源类，包括资源名称、总数、可用数等属性。

public class Resource {
    private String name; // 资源名称
    private int totalNum; // 资源总数
    private int availableNum; // 资源可用数

    // 构造方法
    public Resource(String name, int totalNum, int availableNum) {
        this.name = name;
        this.totalNum = totalNum;
        this.availableNum = availableNum;
    }

    // getter和setter方法
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getTotalNum() {
        return totalNum;
    }

    public void setTotalNum(int totalNum) {
        this.totalNum = totalNum;
    }

    public int getAvailableNum() {
        return availableNum;
    }

    public void setAvailableNum(int availableNum) {
        this.availableNum = availableNum;
    }
}

2.定义进程类，包括进程名称、所需资源数、已分配资源数、需要资源数等属性。

public class Process {
    private String name; // 进程名称
    private int[] need; // 需要资源数
    private int[] allocation; // 已分配资源数
    private boolean finish; // 是否完成

    // 构造方法
    public Process(String name, int[] need, int[] allocation) {
        this.name = name;
        this.need = need;
        this.allocation = allocation;        this.finish = false;
    }

    // getter和setter方法
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int[] getNeed() {
        return need;
    }

    public void setNeed(int[] need) {
        this.need = need;
    }

    public int[] getAllocation() {
        return allocation;
    }

    public void setAllocation(int[] allocation) {
        this.allocation = allocation;
    }

    public boolean isFinish() {
        return finish;
    }

    public void setFinish(boolean finish) {
        this.finish = finish;
    }
}

3.定义银行家算法类，包括银行家算法的主要逻辑。

import java.util.ArrayList;
import java.util.List;

public class BankerAlgorithm {
    private List<Resource> resources; // 资源列表
    private List<Process> processes; // 进程列表

    // 构造方法
    public BankerAlgorithm(List<Resource> resources, List<Process> processes) {
        this.resources = resources;
        this.processes = processes;
    }

    // 银行家算法主要逻辑
    public boolean isSafe() {
        // 初始化工作
        int[] available = new int[resources.size()]; // 可用资源数
        int[][] need = new int[processes.size()][resources.size()]; // 需要资源数
        int[][] allocation = new int[processes.size()][resources.size()]; // 已分配资源数
        boolean[] finish = new boolean[processes.size()]; // 是否完成

        // 初始化available数组
        for (int i = 0; i < resources.size(); i++) {
            available[i] = resources.get(i).getAvailableNum();
        }

        // 初始化need和allocation数组
        for (int i = 0; i < processes.size(); i++) {
            for (int j = 0; j < resources.size(); j++) {
                need[i][j] = processes.get(i).getNeed()[j];
                allocation[i][j] = processes.get(i).getAllocation()[j];
            }
        }

        // 银行家算法主要逻辑
        int count = 0; // 完成进程数
        while (count < processes.size()) {
            boolean flag = false; // 是否找到满足条件的进程
            for (int i = 0; i < processes.size(); i++) {
                if (!finish[i]) {
                    boolean temp = true;
                    for (int j = 0; j < resources.size(); j++) {
                        if (need[i][j] > available[j]) {
                            temp = false;
                            break;
                        }
                    }
                    if (temp) {
                        flag = true;
                        finish[i] = true;
                        count++;
                        for (int j = 0; j < resources.size(); j++) {
                            available[j] += allocation[i][j];
                        }
                    }
                }
            }
            if (!flag) {
                return false;
            }
        }
        return true;
    }
}

4.测试银行家算法。

public class TestBankerAlgorithm {
    public static void main(String[] args) {
        // 初始化资源列表
        List<Resource> resources = new ArrayList<>();
        resources.add(new Resource("A", 10, 3));
        resources.add(new Resource("B", 5, 2));
        resources.add(new Resource("C", 7, 1));

        // 初始化进程列表
        List<Process> processes = new ArrayList<>();
        processes.add(new Process("P1", new int[]{7, 5, 3}, new int[]{0, 1, 0}));
        processes.add(new Process("P2", new int[]{3, 2, 2}, new int[]{2, 0, 0}));
        processes.add(new Process("P3", new int[]{9, 0, 2}, new int[]{3, 0, 2}));
        processes.add(new Process("P4", new int[]{2, 2, 2}, new int[]{2, 1, 1}));
        processes.add(new Process("P5", new int[]{4, 3, 3}, new int[]{0, 0, 2}));

        // 测试银行家算法
        BankerAlgorithm bankerAlgorithm = new BankerAlgorithm(resources, processes);
        if (bankerAlgorithm.isSafe()) {
            System.out.println("系统是安全的");
        } else {
            System.out.println("系统是不安全的");
        }
    }
}