Shortest Job First (SJF) Scheduling Non - Preemptive > Java Program

Computer Organization and Architecture

Shortest Job First (SJF) Scheduling > Java Program

/*
A different approach to CPU scheduling is Shortest job first(sjf) scheduling algorithm.This associates with each process the length of the latter next CPU burst.When the CPU is available it is assigned to the process that has the smallest next CPU burst.if two processes have same length next CPU burst,FCFS scheduling is used to break the tie.Note that a more appropriate term would be the shortest next CPU burst ,because the scheduling is done by examining the length of the next CPU burst because the scheduling is done by examining the length of the next CPU burst of a process,rather than its total length.The real difficulty in Shortest job first(sjf) scheduling algorithm is knowing the length of the next process.Shortest job first(sjf) scheduling algorithm is provably optimal.in that it gives the minimum average waiting time for a given set of processes. */

Non - Preemptive

import java.util.*; 
class SJF 
{ 
public static void main(String args[]) 
{  
Scanner sc=new Scanner(System.in); 
int n,BT[],WT[],TAT[], OUT[]; 
System.out.println("Enter no of process"); 
n=sc.nextInt(); 
BT=new int[n+1]; 
WT=new int[n+1]; 
TAT=new int[n+1];
OUT=new int[n+1];
float AWT=0;
float ATAT=0;

System.out.println("Enter Burst time for each process"); 
for(int i=0;i<n;i++) 
{ 
System.out.println("Enter BT for process "+(i+1)); 
BT[i]=sc.nextInt(); 
OUT[i]=i+1;
}

for(int i=0;i<n;i++) 
{
WT[i]=0; TAT[i]=0; 
} 
int temp; 
for(int i=0;i<n-1;i++) 
{
for(int j=0;j<n-1;j++) 
{ 
if(BT[j]>BT[j+1])    
{
temp=BT[j]; 
BT[j]=BT[j+1]; 
BT[j+1]=temp; 
temp=OUT[j]; 
OUT[j]=OUT[j+1]; 
OUT[j+1]=temp; 
}
}
} 

for(int i=0;i<n;i++) 
{
    TAT[i]=BT[i]+WT[i]; 
    WT[i+1]=TAT[i]; 
} 
TAT[n]=WT[n]+BT[n]; 

for(int j=0;j<n;j++) {
    TAT[j]=WT[j]+BT[j];
    AWT+=WT[j]; 
}



System.out.println("  PROCESS   BT      WT      TAT     "); 
for(int i=0;i<n;i++) 
System.out.println("    "+ OUT[i] + "       "+BT[i]+"       "+WT[i]+"       "+TAT[i]); 

AWT=AWT/n; 
System.out.println("***********************************************"); 
System.out.println("Avg waiting time="+AWT+"\n***********************************************"); 

for(int i=0;i<n;i++) 
{ 
TAT[i]=WT[i]+BT[i]; 
ATAT=ATAT+TAT[i]; 
}

ATAT=ATAT/n; 
System.out.println("***********************************************"); 
System.out.println("Avg turn around time="+ATAT+"\n***********************************************"); 
} 
}


 /* O/P for Shortest job first(sjf) scheduling algorithm is : 
Enter no of process
3
Enter Burst time for each process
Enter BT for process 1
24
Enter BT for process 2
3
Enter BT for process 3
3
  PROCESS   BT      WT      TAT     
    2       3       0       3
    3       3       3       6
    1       24       6       30
***********************************************
Avg waiting time=3.0
***********************************************
***********************************************
Avg turn around time=13.0
***********************************************
BUILD SUCCESSFUL (total time: 8 seconds)

*/