文章目錄
- 一、FCFS的介紹
- 二、代碼示範
- 三、代碼分析
- 1.使用節點模拟程序
- 2.SimulateFCFS（核心模拟FCFS類）
- 3.建立一個節點為n的隊列（模拟就緒隊列）
- 4.核心計算分析
- 5.輸入到達時間和服務時間（模拟程序到達和服務)
- 6.出隊列（模拟完成所有程序工作）
一、FCFS的介紹
先來先服務的排程算法：最簡單的排程算法，既可以用于作業排程 ，也可以用于程式排程，當作業排程中采用該算法時，系統将按照作業到達的先後次序來進行排程，優先從後備隊列中，選擇一個或多個位于隊列頭部的作業，把他們調入記憶體，配置設定所需資源、建立程序，然後放入“就緒隊列”,直到該程序運作到完成或發生某事件堵塞後，程序排程程式才将處理機配置設定給其他程序。
簡單了說就是如同名字 “先來先服務” ；
二、代碼示範
package com.zsh.blog;
import java.util.Scanner;
/**
* @author:抱着魚睡覺的喵喵
* @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、代碼分析
1.使用節點模拟程序
因為需要計算完成時間、周轉時間、帶權周轉時間，是以需要事先給出每個程序到達時間和服務時間
模拟時至少需要以下幾個屬性（Queue類對象模拟程序）
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類）
3.建立一個節點為n的隊列（模拟就緒隊列）
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(); //建立節點數為n的隊列
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);//這個自定義的函數主要用來輸入程序的到達時間和服務時間
calTime(arr); //該自定義函數用來計算完成時間、周轉時間、帶權周轉時間
temp.next = arr;
temp = arr; //進行節點連接配接
}
this.tail = arr;
System.out.println("Simulation allocation is successful!");
} 4.核心計算分析
//timer是全局變量，用來計算完成時間（解決上面的問題）
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.輸入到達時間和服務時間（模拟程序到達和服務)
public void keyBordInput(Queue arr, Scanner scanner) {
arr.processName = scanner.next();
arr.arrTime = scanner.nextInt();
arr.serviceTime = scanner.nextInt();
} 6.出隊列（模拟完成所有程序工作）
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;
}
}