文章目录
- 一、FCFS的介绍
- 二、代码演示
- 三、代码分析
- 1.使用节点模拟进程
- 2.SimulateFCFS（核心模拟FCFS类）
- 3.创建一个节点为n的队列（模拟就绪队列）
- 4.核心计算分析
- 5.输入到达时间和服务时间（模拟进程到达和服务)
- 6.出队列（模拟完成所有进程工作）
一、FCFS的介绍
先来先服务的调度算法：最简单的调度算法，既可以用于作业调度 ，也可以用于程序调度，当作业调度中采用该算法时，系统将按照作业到达的先后次序来进行调度，优先从后备队列中，选择一个或多个位于队列头部的作业，把他们调入内存，分配所需资源、创建进程，然后放入“就绪队列”,直到该进程运行到完成或发生某事件堵塞后，进程调度程序才将处理机分配给其他进程。
简单了说就是如同名字 “先来先服务” ；
二、代码演示
package com.zsh.blog;
import java.util.Scanner;
/**
* @author:抱着鱼睡觉的喵喵
* @date:2021/3/19
* @description:
*/
public class SimulateSystem {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
SimulateFCFS simulateFCFS = new SimulateFCFS();
boolean flag = true;
char at = ' ';
System.out.println("a:Simulate multiple processes to form a queue");
System.out.println("b:Assign a process to the queue");
System.out.println("d:Complete all process work");
System.out.println("e:Exit the simulated system");
while (flag) {
System.out.println("Please enter your instructions：");
at = scanner.next().charAt(0);
switch (at) {
case 'a':
simulateFCFS.createQueue();
break;
case 'b':
simulateFCFS.assignProcess();
break;
case 'd':
simulateFCFS.finishAllProcessTask();
return;
case 'e':
System.out.println("Simulated is end~");
return;
default:
System.out.println("Your input is wrong, please re-enter！");
break;
}
}
}
}
class Queue {
int arrTime; //timeOfArrival
int serviceTime; //timeOfService
int finishTime; //timeOfComplish
int turnTime; //timeOfTurnaround
double weightTurnTime; //timeOfWeightTurnaround
String processName; //process number
Queue next;
public Queue(int arrTime, int serviceTime, String processName) {
this.arrTime = arrTime;
this.serviceTime = serviceTime;
this.processName = processName;
}
public Queue() {
}
}
/**
* Simulate FCFS algorithm class
*/
class SimulateFCFS {
private Queue head = new Queue(-1, -1, null);
private int timer = 0;
private Queue tail = head;
public void createQueue() {
Queue arr = null;
Queue temp = head;
Scanner scanner = new Scanner(System.in);
System.out.printf("Please enter the number of process tasks to initialize the simulation:");
int n = scanner.nextInt();
for (int i = 1; i <= n; i++) {
System.out.printf("Please enter the process number, start time, and service time of the %d process:",i);
arr = new Queue();
keyBordInput(arr, scanner);
calTime(arr);
temp.next = arr;
temp = arr;
}
this.tail = arr;
System.out.println("Simulation allocation is successful!");
}
/**
* Completion time of calculation process - Turnaround time - Weighted turnaround time
* @param arr
*/
public void calTime(Queue arr) {
Queue temp = arr;
if (this.timer < temp.arrTime) {
this.timer = arr.arrTime;
} else {
if (timer == 0) {
this.timer = temp.arrTime;
}
}
temp.finishTime = temp.serviceTime + this.timer;
temp.turnTime = temp.finishTime - temp.arrTime;
temp.weightTurnTime = (temp.turnTime * 1.0) / (temp.serviceTime * 1.0);
this.timer += temp.serviceTime;
}
/**
* Process number，arrival time，service time entered from the keyboard
* @param arr
* @param scanner
*/
public void keyBordInput(Queue arr, Scanner scanner) {
arr.processName = scanner.next();
arr.arrTime = scanner.nextInt();
arr.serviceTime = scanner.nextInt();
}
/**
* Assign a process to the queue
*/
public void assignProcess() {
Queue newProcess = new Queue();
Scanner scanner = new Scanner(System.in);
System.out.printf("Please enter the add process number,start time,and service time of the process:");
keyBordInput(newProcess, scanner);
calTime(newProcess);
this.tail.next = newProcess;
this.tail = newProcess;
}
/**
* Complish a task of process from the queue
*/
// public void finishProcessTask() {
// Queue workingProcess = head;
//
// }
/**
* Complish all task of process from the queue
*/
public void finishAllProcessTask() {
if (isEmpty()) {
return;
}
Queue cur = head.next;
System.out.println("Process number========Arrive time======Service time=======finish Time=======Turn time======WeightTurn time");
while (true) {
System.out.printf("\t\t%s\t\t\t\t%d\t\t\t\t\t%d\t\t\t\t\t%d\t\t\t\t%d\t\t\t\t%f",cur.processName,cur.arrTime,cur.serviceTime,cur.finishTime,cur.turnTime,cur.weightTurnTime);
System.out.println();
if (cur.next == null) {
break;
}
cur = cur.next;
}
}
public boolean isEmpty() {
if (head.next == null) {
System.out.println("Queue is null!");
return true;
}
return false;
}
} 
三、代码分析
1.使用节点模拟进程
因为需要计算完成时间、周转时间、带权周转时间，所以需要事先给出每个进程到达时间和服务时间
模拟时至少需要以下几个属性（Queue类对象模拟进程）
class Queue {
int arrTime; //timeOfArrival
int serviceTime; //timeOfService
int finishTime; //timeOfComplish
int turnTime; //timeOfTurnaround
double weightTurnTime; //timeOfWeightTurnaround
String processName; //process number
Queue next;
public Queue(int arrTime, int serviceTime, String processName) {
this.arrTime = arrTime;
this.serviceTime = serviceTime;
this.processName = processName;
}
public Queue() {
}
} 2.SimulateFCFS（核心模拟FCFS类）
3.创建一个节点为n的队列（模拟就绪队列）
public void createQueue() {
Queue arr = null;
Queue temp = head;
Scanner scanner = new Scanner(System.in);
System.out.printf("Please enter the number of process tasks to initialize the simulation:");
int n = scanner.nextInt(); //创建节点数为n的队列
for (int i = 1; i <= n; i++) {
System.out.printf("Please enter the process number, start time, and service time of the %d process:",i);
arr = new Queue();
keyBordInput(arr, scanner);//这个自定义的函数主要用来输入进程的到达时间和服务时间
calTime(arr); //该自定义函数用来计算完成时间、周转时间、带权周转时间
temp.next = arr;
temp = arr; //进行节点连接
}
this.tail = arr;
System.out.println("Simulation allocation is successful!");
} 4.核心计算分析
//timer是全局变量，用来计算完成时间（解决上面的问题）
public void calTime(Queue arr) {
Queue temp = arr;
if (this.timer < temp.arrTime) {
this.timer = arr.arrTime;
} else {
if (timer == 0) {
this.timer = temp.arrTime;
}
}
temp.finishTime = temp.serviceTime + this.timer;
temp.turnTime = temp.finishTime - temp.arrTime;
temp.weightTurnTime = (temp.turnTime * 1.0) / (temp.serviceTime * 1.0);
this.timer += temp.serviceTime;
} 5.输入到达时间和服务时间（模拟进程到达和服务)
public void keyBordInput(Queue arr, Scanner scanner) {
arr.processName = scanner.next();
arr.arrTime = scanner.nextInt();
arr.serviceTime = scanner.nextInt();
} 6.出队列（模拟完成所有进程工作）
public void finishAllProcessTask() {
if (isEmpty()) {
return;
}
Queue cur = head.next;
System.out.println("Process number========Arrive time======Service time=======finish Time=======Turn time======WeightTurn time");
while (true) {
System.out.printf("\t\t%s\t\t\t\t%d\t\t\t\t\t%d\t\t\t\t\t%d\t\t\t\t%d\t\t\t\t%f",cur.processName,cur.arrTime,cur.serviceTime,cur.finishTime,cur.turnTime,cur.weightTurnTime);
System.out.println();
if (cur.next == null) {
break;
}
cur = cur.next;
}
}