用java语言，模拟实现操作系统的进程调度算法，先来先服务，高优先级、高响应比、时间片轮转和短作业

构思算法的实现过程。

①先来先服务算法
一开始我从最简单的先来先服务开始想，既然要排序进程链表的执行顺序，肯定要将链表的头head作为参数传入到方法中。其次为了之后方便一次性检验多种算法，传入进来的head链表我不会对它进行任何改变。所以创建一个新链表head2用CreateHead方法将链表进行复制，这样我就可以拿head2这个复制品随便搞，也不会影响之后调用其他算法，因为head没变。
当我拿到复制链表head2之后，要对他进行先来先服务算法排序，肯定要比较所有进程的到达时间，从到达时间最小的进程先开始执行，需要注意的是将某个进程执行完毕之后，要将它从链表中移除，以确保下一次查找的正确性。所以我用一个大循环，循环次数是链表的结点数，每一次循环都找到本次循环到达时间最小的那个结点，然后将这个结点的所有进程信息进行更新，包括完成时间，周转时间，带权周转时间，打印所有的信息到控制台。并且更新一下总时间线start(一开始为0，每次运行一个进程，它的值都加上这个进程的运行时间，相当于总时间线）。最后将这个结点从链表中删除，再次循环从剩余的节点中找到达时间最小的结点，直到所有结点都被删除了。那么所有结点的执行顺序也已经全部被打印到控制台上了。每次循环都记录周转时间和带权周转时间。最后循环结束计算一下平均值。下面是算法流程图：

②短作业优先算法
短作业优先自然要选择运行时间最短的进程先执行，和上面的算法流程图大体一致，就是要找出链表中运行时间最短的节点。并且要注意的是如果最短运行时间的进程的到达时间很迟，而有一个运行时间较长的进程先到达了，就不能让CPU等着。应该先执行到达的进程，等到这个进程执行完毕之后，再次找运行时间最短的进程。直到程序退出。
③高优先级优先算法
高优先级和前两种也类似，主要是找到最高优先级的进程先运行，而且也要和第二种算法一样注意进程的到达时间。
④高响应比优先算法
此算法和前三种稍有不同，虽然大体流程相同，但是响应比有自己的计算公式，响应比 = （等待时间+要求服务时间）/ 要求服务时间。
我封装了一个方法专门求响应比，所以也可以和上面三种程序一样先找到响应比最高的进程运行。需要注意的是，每一个进程运行完毕之后响应比都会发生变化。
⑤时间片轮转算法
这个算法我想它大体是个先来先服务一样的，所以我将所有进程一开始按到达时间排序，因为每次时间片执行完毕进程不一定结束，所以给进程的节点中添加两个新属性int newarrival和int newruntime用来保存更新之后的到达时间和运行时间，每次时间片执行完毕，这个进程的到达时间就是此刻，然后将它的到达时间和链表中所有的进程的到达时间进行比较，插入它比它小和比它大的到达时间之间，如果遇到相等的到达时间就插入到本来存在节点的后面。然后本次时间片结束，头指针向后移动运行下一个排队的进程节点。

源代码如下

import java.util.Scanner;
class Node{
    String name;
    int priority;
    int runtime;
    int arrivaltime;
    int starttime;
    int endtime;
    int turntime;  //周转时间
    double dturntime;  //带权周转时间
    Node nextnode;
    int statu;
    int newarrival;
    int newruntime;

    public Node(String name,int priority,int runtime,int arrivaltime, int starttime, int endtime, int turntime, double dturntime){
        this.name = name;
        this.priority = priority;
        this.runtime = runtime;
        this.arrivaltime = arrivaltime;
        this.nextnode = null;
        this.starttime = starttime;
        this.endtime = endtime;
        this.turntime = turntime;
        this.dturntime = dturntime;
        this.newarrival = arrivaltime;
        this.newruntime = runtime;
    }

}

class Create{
    public Node createNode(Node head, String name, int priority, int runtime, int arrivaltime, int starttime, int endtime, int turntime, double dturntime){

        if(head == null){
            Node node = new Node(name,priority,runtime,arrivaltime,starttime,endtime,turntime,dturntime);
            head = node;
            return head;
        }
        Node cur = head;
        while(cur.nextnode!=null){
            cur = cur.nextnode;
        }
        Node node = new Node(name,priority,runtime,arrivaltime,starttime,endtime,turntime,dturntime);
        cur.nextnode = node;
        return head;
    }

    public void check(Node head){
        if(head == null){
            System.out.println("当前没有节点信息");
            return;
        }
        Node cur = head;
        while(cur!=null){
            System.out.println("名字:"+cur.name+"、优先级:"+cur.priority+"、运行时间:"+cur.runtime+"、到达时间"+cur.arrivaltime);
            cur = cur.nextnode;
        }
    }
}

class Algorithm{
    private Node pre = null;
    private Node prev = null;
    private Node min = null;
    private int num = 0;
    private int start = 0;
    private double nums = 0.0;
    private int count = 0;
    private static Create create = new Create();
    private static Node CreateHead(Node head){
        Node head2 = null;
        Node cur = head;
        while(cur!=null){
            head2 = create.createNode(head2,cur.name,cur.priority,cur.runtime,cur.arrivaltime,cur.starttime,cur.endtime,cur.turntime,cur.dturntime);
            cur = cur.nextnode;
        }
        return head2;
    }

    private void endFun(){
        System.out.println("平均周转时间:" + (double) this.num / this.count + "平均带权周转时间:" + this.nums / this.count);
        this.start = 0;
        this.num = 0;
        this.nums = 0;
        this.count = 0;
    }

    private static Node toolMethod(Node min,Node prev,int start,Node head){
        min.starttime = start;
        min.endtime = min.starttime + min.runtime;
        min.turntime = min.endtime - min.arrivaltime;
        min.dturntime = (double) min.turntime / (double) min.runtime;
        System.out.println("名字:" + min.name + "、优先级:" + min.priority + "、运行时间:" + min.runtime + "、到达时间" + min.arrivaltime + "、开始时间:" + min.starttime + "、结束时间:" + min.endtime + "、周转时间:" + min.turntime + "、带权周转时间:" + min.dturntime);
        if (prev == null) {
            if (min.nextnode == null) {
                return null;
            }
            return min.nextnode;
        } else {
            prev.nextnode = min.nextnode;
        }
        return head;
    }

    private static Node findMin(Node head){
        Node cur = head;
        Node real = null;
        int mintime = cur.arrivaltime;
        while(cur!=null){
            if(cur.arrivaltime<=mintime){
                mintime = cur.arrivaltime;
                real = cur;
            }
            cur = cur.nextnode;
        }
        return real;
    }

    public void Fcfs(Node head) {
        Node head2 = CreateHead(head);
        while (head2 != null) {
            min = null;
            pre = null;
            Node cur = head2;
            int mintime = cur.arrivaltime;
            while (cur != null) {
                if (cur.arrivaltime <= mintime) {
                    mintime = cur.arrivaltime;
                    prev = pre;
                    min = cur;
                }
                pre = cur;
                cur = cur.nextnode;
            }
            if (min.arrivaltime > start) {
                start = min.arrivaltime;
            }
            head2 = toolMethod(min,prev,start,head2);
            start = start + min.runtime;
            num += min.turntime;
            nums += min.dturntime;
            count++;
        }
        this.endFun();
    }

    public void Priority(Node head){
        Node head2 = CreateHead(head);
        while(head2!=null){
            min = null;
            pre = null;
            Node cur = head2;
            int mintime = 0;
            while(cur!=null){
                if(cur.priority >= mintime && cur.arrivaltime <= start){
                    mintime = cur.priority;
                    prev = pre;
                    min = cur;
                }
                pre = cur;
                cur = cur.nextnode;
            }
            if(min == null){
                min = findMin(head2);
            }
            if(min.arrivaltime > start){
                start = min.arrivaltime;
            }
            head2 = toolMethod(min,prev,start,head2);
            start = start + min.runtime;
            num += min.turntime;
            nums += min.dturntime;
            count++;
        }
        this.endFun();
    }

    public void ShortProcess(Node head){
        Node head2 = CreateHead(head);
        while(head2!=null){
            min = null;
            pre = null;
            Node cur = head2;
            int mintime = 1000;
            while(cur!=null){
                if(cur.runtime <= mintime && cur.arrivaltime <= start){
                    mintime = cur.runtime;
                    prev = pre;
                    min = cur;
                }
                pre = cur;
                cur = cur.nextnode;
            }
            if(min == null){
                min = findMin(head2);
            }
            if(min.arrivaltime > start){
                start = min.arrivaltime;
            }
            head2 = toolMethod(min,prev,start,head2);
            start = start + min.runtime;
            num += min.turntime;
            nums += min.dturntime;
            count++;
        }
        this.endFun();
    }

    private static double resRatio(Node node,int start){
        int waittime = start - node.arrivaltime;
        return (double)waittime/node.runtime;
    }
    public void Hreponse(Node head){
        Node head2 = CreateHead(head);
        while(head2!=null){
            min = null;
            pre = null;
            Node cur = head2;
            double mintime = 0.0;
            while(cur!=null){
                double resratio = resRatio(cur,start);
                if(resratio >= mintime && cur.arrivaltime <= start){
                    mintime = resratio;
                    prev = pre;
                    min = cur;
                }
                pre = cur;
                cur = cur.nextnode;
            }
            if(min == null){
                min = findMin(head2);
            }
            if(min.arrivaltime > start){
                start = min.arrivaltime;
            }
            head2 = toolMethod(min,prev,start,head2);
            start = start + min.runtime;
            num += min.turntime;
            nums += min.dturntime;
            count++;
        }
        this.endFun();
    }

    public static Node QueueHead(Node head){
        Node cur = head;
        Node nodemin = null;
        Node head2 = null;
        int min = 1000;
        int count = 0;
        while(cur!=null){
            count++;
            cur = cur.nextnode;
        }
        while(count!=0) {
            min = 1000;
            cur = head;
            while (cur != null) {
                if (cur.arrivaltime < min && cur.statu == 0) {
                    nodemin = cur;
                    min = cur.arrivaltime;
                }
                cur = cur.nextnode;
            }
            nodemin.statu = 1;
            count--;
            head2 = create.createNode(head2,nodemin.name,nodemin.priority,nodemin.runtime,nodemin.arrivaltime,nodemin.starttime,nodemin.endtime,nodemin.turntime,nodemin.dturntime);
        }
        return head2;
    }

    public static void insert(Node head,Node min){
        Node cur = head;
        Node pre = null;
        while(cur!=null){
            if(cur.arrivaltime > min.newarrival){
                pre.nextnode = min;
                min.nextnode = cur;
                return;
            }
            pre = cur;
            cur = cur.nextnode;
        }
        pre.nextnode = min;
        min.nextnode = cur;
    }

    public void Roundrobin(Node head,int Rtime){
        Node newnode = null;
        Node head2 = QueueHead(head);
        create.check(head2);
        System.out.println(head2.newruntime);
        System.out.println(head2.newarrival);
        while(head2!=null){
            min = head2;
            if(min.arrivaltime > start){
                start = min.arrivaltime;
            }
            if(min.newruntime > Rtime){
                min.newruntime -= Rtime;
                start += Rtime;
                min.newarrival += Rtime;
                newnode = new Node(min.name,min.priority,min.runtime,min.arrivaltime,min.starttime,min.endtime,min.turntime,min.dturntime);
                newnode.newarrival = min.newarrival;
                newnode.newruntime = min.newruntime;
                insert(head2,newnode);
                head2 = min.nextnode;
            }else{
                start += min.newruntime;
                min.endtime = start;
                min.turntime = min.endtime - min.arrivaltime;
                min.dturntime = (double) min.turntime / (double) min.runtime;
                head2 = min.nextnode;
                num += min.turntime;
                nums += min.dturntime;
                count++;
                System.out.println("名字:" + min.name + "、优先级:" + min.priority + "、运行时间:" + min.runtime + "、到达时间" + min.arrivaltime + "、开始时间:" + min.starttime + "、结束时间:" + min.endtime + "、周转时间:" + min.turntime + "、带权周转时间:" + min.dturntime);
            }
        }
        this.endFun();
    }
}

public class Test {
    public static void dispatchMenu(Node head){

        Scanner sc = new Scanner(System.in);
        Algorithm al = new Algorithm();
        int count = 1;
        while(count == 1){
            System.out.println("请选择调度算法:");
            System.out.println("1.先来先服务算法");
            System.out.println("2.短作业优先算法");
            System.out.println("3.高优先级优先算法");
            System.out.println("4.高响应比优先算法");
            System.out.println("5.时间片轮转算法");
            System.out.println("0.退出");
            int num = sc.nextInt();
            switch(num){
                case 1:al.Fcfs(head);
                    break;
                case 2:al.ShortProcess(head);
                    break;
                case 3:al.Priority(head);
                    break;
                case 4:al.Hreponse(head);
                    break;
                case 5:al.Roundrobin(head,1);
                    break;
                case 0:count = 0;
                    break;
                default:System.out.println("输入错误请重新输入");
            }
        }
    }

    public static void mainMenu(){
        Create create = new Create();
        Node head = null;

        Scanner sc = new Scanner(System.in);

        int count1 = 1;
        while(count1 == 1){
            System.out.println("请选择你需要的服务:");
            System.out.println("1.添加新进程");
            System.out.println("2.使用调度算法进行排序");
            System.out.println("3.查看当前进程信息");
            System.out.println("0.退出");
            int num = sc.nextInt();
            switch(num){
                case 1:
                    String name;
                    int priority;
                    int runtime;
                    int arrivaltime;
                    System.out.println("请输入进程名字:");
                    name = sc.next();
                    System.out.println("请输入进程优先级:");
                    priority = sc.nextInt();
                    System.out.println("请输入进行运行时间:");
                    runtime = sc.nextInt();
                    System.out.println("请输入进程到达时间:");
                    arrivaltime = sc.nextInt();
                    head = create.createNode(head,name,priority, runtime,arrivaltime,0,0,0,0);
                    break;
                case 2:Test.dispatchMenu(head);
                    break;
                case 3:create.check(head);
                    break;
                case 0:count1 = 0;
                    break;
                default:System.out.println("输入错误请重新输入");
            }
        }
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Test.mainMenu();
    }
}