SJF.java

import java.util.*;

public class SJF {
     class Process{
        int ProcessNo;
        int ArrivalTime;
        int BurstTime;
        int ComplitionTime;
        int TurnAroundTime;
        int WaitingTime;
        int ResponseTime;

        Process(int ProcessNo, int ArrivalTime, int BurstTime){
            this.ProcessNo=ProcessNo;
            this.ArrivalTime=ArrivalTime;
            this.BurstTime=BurstTime;
        }

    }

    Comparator<Process> comparator = new Comparator<>(){
        public int compare(Process p1, Process p2){
            if(p1.BurstTime != p2.BurstTime){
                return Integer.compare(p1.BurstTime, p2.BurstTime);
            }
            else{
                return Integer.compare(p1.ArrivalTime, p2.ArrivalTime);
            }
        }
    };

    public void sjfSchedulingAlgorithm(Process[] processes){

        Arrays.sort(processes, Comparator.comparingInt(p -> p.ArrivalTime));
        PriorityQueue<Process>queue=new PriorityQueue<>(comparator);

        List<Process>ans=new ArrayList<>();
        List<String>ganttChart=new ArrayList<>();

        int startTime=0;
        int i=0;

        while(i<processes.length || !queue.isEmpty()){

            while(i<processes.length && processes[i].ArrivalTime <= startTime){
                queue.add(processes[i]);
                i++;
            }

            if(!queue.isEmpty()){
                Process curr=queue.poll();

                curr.ComplitionTime = startTime + curr.BurstTime;
                curr.TurnAroundTime = curr.ComplitionTime - curr.ArrivalTime;
                curr.WaitingTime = curr.TurnAroundTime - curr.BurstTime;
                curr.ResponseTime = startTime - curr.ArrivalTime;

                ans.add(curr);
                ganttChart.add("P"+String.valueOf(curr.ProcessNo));
                startTime+=curr.BurstTime;
            }
            else{
                ganttChart.add("CPU Ideal");
                startTime++;
            }
        }

        System.out.println("Process No.  |AT   |BT    |CT    |TAT   |WT   |RT");
        for(i=0;i<ans.size();i++){
            Process p=ans.get(i);
            System.out.println("P"+p.ProcessNo + "           |" 
            + p.ArrivalTime + "    |" 
            + p.BurstTime + "     |" 
            + p.ComplitionTime + "     |" 
            + p.TurnAroundTime + "    |" 
            + p.WaitingTime + "    |" 
            + p.ResponseTime);
        }

        System.out.println("\nGantt Chart of SJF is as below");
        System.out.println(ganttChart);
    }


    public static void main(String[] a){
        Scanner sc=new Scanner(System.in);
        SJF sjf=new SJF();

        System.out.println("Enter the total no. of process to schedule");
        int noOfProcess=sc.nextInt();

        Process[] processes=new Process[noOfProcess];

        System.out.println("Enter the arrival time of each pocess along with its brust time");
        for(int i=0;i<noOfProcess;i++){
            processes[i]=sjf.new Process(i, sc.nextInt(), sc.nextInt());
        }

        sjf.sjfSchedulingAlgorithm(processes);


    }
}