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package Others;

/**

* <h2>Shortest job first.</h2>

* <p>Shortest job first (SJF) or shortest job next, is a scheduling policy that selects the waiting

* process with the smallest execution time to execute next Shortest Job first has the advantage of

* having minimum average waiting time among all scheduling algorithms. It is a Greedy Algorithm. It

* may cause starvation if shorter processes keep coming. This problem has been solved using the

* concept of aging.

* @author shivg7706

* @since 2018/10/27

import java.util.*;

import java.util.ArrayList;

import java.util.Comparator;

import java.util.Scanner;

class Process {

public int pid;

public int arrivalTime;

public int burstTime;

public int priority;

public int turnAroundTime;

public int waitTime;

public int remainingTime;

}

class Schedule {

private int noOfProcess;

private int timer = 0;

private ArrayList<Process> processes;

private ArrayList<Process> remainingProcess;

private ArrayList<Integer> gantChart;

private float burstAll;

private Map<Integer, ArrayList<Process>> arrivals;

Schedule() {

Scanner in = new Scanner(System.in);

processes = new ArrayList<Process>();

remainingProcess = new ArrayList<Process>();

gantChart = new ArrayList<>();

arrivals = new HashMap<>();

System.out.print("Enter the no. of processes: ");

noOfProcess = in.nextInt();

System.out.println("Enter the arrival, burst and priority of processes");

for (int i = 0; i < noOfProcess; i++) {

Process p = new Process();

p.pid = i;

p.arrivalTime = in.nextInt();

p.burstTime = in.nextInt();

p.priority = in.nextInt();

p.turnAroundTime = 0;

p.waitTime = 0;

p.remainingTime = p.burstTime;

if (arrivals.get(p.arrivalTime) == null) {

arrivals.put(p.arrivalTime, new ArrayList<Process>());

}

arrivals.get(p.arrivalTime).add(p);

processes.add(p);

burstAll += p.burstTime;

}

in.close();

}

void startScheduling() {

processes.sort(

new Comparator<Process>() {

@Override

public int compare(Process a, Process b) {

return a.arrivalTime - b.arrivalTime;

}

});

while (!(arrivals.size() == 0 && remainingProcess.size() == 0)) {

removeFinishedProcess();

if (arrivals.get(timer) != null) {

remainingProcess.addAll(arrivals.get(timer));

arrivals.remove(timer);

}

remainingProcess.sort(

new Comparator<Process>() {

private int alpha = 6;

private int beta = 1;

@Override

public int compare(Process a, Process b) {

int aRem = a.remainingTime;

int bRem = b.remainingTime;

int aprior = a.priority;

int bprior = b.priority;

return (alpha * aRem + beta * aprior) - (alpha * bRem + beta * bprior);

}

});

int k = timeElapsed(timer);

ageing(k);

timer++;

}

System.out.println("Total time required: " + (timer - 1));

}

void removeFinishedProcess() {

ArrayList<Integer> completed = new ArrayList<Integer>();

for (int i = 0; i < remainingProcess.size(); i++) {

if (remainingProcess.get(i).remainingTime == 0) {

completed.add(i);

}

for (int i = 0; i < completed.size(); i++) {

int pid = remainingProcess.get(completed.get(i)).pid;

processes.get(pid).waitTime = remainingProcess.get(completed.get(i)).waitTime;

remainingProcess.remove(remainingProcess.get(completed.get(i)));

}

public int timeElapsed(int i) {

if (!remainingProcess.isEmpty()) {

gantChart.add(i, remainingProcess.get(0).pid);

remainingProcess.get(0).remainingTime--;

return 1;

}

return 0;

}

public void ageing(int k) {

for (int i = k; i < remainingProcess.size(); i++) {

remainingProcess.get(i).waitTime++;

if (remainingProcess.get(i).waitTime % 7 == 0) {

remainingProcess.get(i).priority--;

}

public void solve() {

System.out.println("Gant chart ");

for (int i = 0; i < gantChart.size(); i++) {

System.out.print(gantChart.get(i) + " ");

}

System.out.println();

float waitTimeTot = 0;

float tatTime = 0;

for (int i = 0; i < noOfProcess; i++) {

processes.get(i).turnAroundTime = processes.get(i).waitTime + processes.get(i).burstTime;

waitTimeTot += processes.get(i).waitTime;

tatTime += processes.get(i).turnAroundTime;

System.out.println(

"Process no.: "

+ i

+ " Wait time: "

+ processes.get(i).waitTime

+ " Turn Around Time: "

+ processes.get(i).turnAroundTime);

}

System.out.println("Average Waiting Time: " + waitTimeTot / noOfProcess);

System.out.println("Average TAT Time: " + tatTime / noOfProcess);

System.out.println("Throughput: " + (float) noOfProcess / (timer - 1));

}

public class SJF {

public static void main(String[] args) {

Schedule s = new Schedule();

s.startScheduling();

s.solve();

}

Java/Others/SJF.java at master · primary-code-test/Java · GitHub

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