Java program to simulate FIFO and LRU page replacement algorithms

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Scanner;

import javax.swing.JFileChooser;

/**
 * This class reads a user chosen file for the reference string
 * (there should be spaces between the values in the string)
 * and simulates the selected page replacement policy i.e.
 * FIFO or LRU. It displays the status of page frames at each
 * new value in the string and saves the paging report in a plain
 * text file.
 * @author Dixit Bhatta
 * **/
public class pgReplace {

public static void main(String[] args) throws IOException {
ArrayList<Integer> ref = new ArrayList<Integer>();//creating new HashSet

try {
Scanner filein = new Scanner(getInputFileNameFromUser()); //open file
while(filein.hasNext()) {
String frame = filein.next();
int frm = Integer.parseInt(frame);
ref.add(frm);// add the integers to HashSet.
}//end of while

filein.close();//close the file

} catch (FileNotFoundException e) {
System.err.println("FileNotFoundException: " + e.getMessage());
}

//display the size if it the set is not empty
if(!ref.isEmpty()){
int size = ref.size();
System.out.println("The length of the Reference String is: " + size);
}
//printing the read reference string using an iterator
Iterator<Integer> iter = ref.iterator();
while (iter.hasNext())
System.out.print(iter.next() +" ");

//converting the arraylist to an array
Integer frame[] = new Integer[ref.size()];
   frame = ref.toArray(frame);

   System.out.printf("\nSelect the Page Replacement Algorithm: ");
   System.out.printf("\n1.FIFO\n2.LRU\n? ");

   Scanner sc = new Scanner(System.in);
   while (!sc.hasNextInt()) {
       sc.next(); // discard next token, which isn't a valid int
   }
   int ch = sc.nextInt();

switch(ch){
   case 1: fifo(frame,ref.size());
    break;
   case 2: lru(frame,ref.size());
    break;
   default: System.out.printf("\nInvlaid Choice");
   }
 
}
/**Simulates LRU page replacement for given reference string
* @throws IOException **/
public static void lru(Integer[] page, int n) throws IOException {
int [] frame = new int[10];
int []used = new int[10];
int index = 0;
int i,j,k,temp;
int flag=0,pf=0;
BufferedWriter write = new BufferedWriter(new FileWriter("file.txt"));
PrintWriter out = new PrintWriter(write);
System.out.printf("\tLRU Page Replacement");
System.out.printf("\nEnter number of Frames: ");
Scanner sc = new Scanner(System.in);
   while (!sc.hasNextInt()) {
       sc.next(); // discard next token, which isn't a valid int
   }
   int nf = sc.nextInt();
for(i=0;i<nf;i++)
frame[i]= -1;

for(i=0;i<n;i++){
flag=0;
for(j=0;j<nf;j++){
if(frame[j]==page[i]){//no fault
System.out.printf("\n%d: ", page[i]);
out.printf("\n%d: ", page[i]);
flag=1;
break;
}
}
if(flag==0){//fault occurs
for(j=0;j<nf;j++)
used[j]=0;//all unused initially
//moving through pages and searching recently used pages
try{
for(j = 0,temp= i-1;j < nf-1;j++,temp--){
for(k = 0;k < nf;k++){
if(frame[k]==page[temp])
used[k]=1;
//mark the recently used pages
}
}
}
catch(ArrayIndexOutOfBoundsException e){
}
for(j=0;j<nf;j++)
if(used[j]==0)
index=j;
//replace the lru page with new page
frame[index]=page[i];
System.out.printf("\n%d: ", page[i]);
System.out.printf("--->F ");
out.printf("\n%d: ", page[i]);
out.printf("--->F ");
pf++;//no of page faults
}

for(k= nf-1;k>=0;k--)
if(frame[k] != -1){
System.out.printf(" %d",frame[k]);//print frames
out.printf(" %d",frame[k]);
}
}

System.out.printf("\nNumber of page faults is: %d ",pf);
out.printf("\nNumber of page faults is: %d ",pf);
out.close();
write.close();
}

/**Simulates FIFO page replacement for given reference string
* @throws IOException **/
public static void fifo(Integer[] pages, int pg) throws IOException {
int [] frame = new int[25];
int i,k,avail,count=0;
BufferedWriter write = new BufferedWriter(new FileWriter("file.txt"));
PrintWriter out = new PrintWriter(write);
System.out.printf("\tFIFO Page Replacement");
System.out.printf("\nEnter number of Frames: ");
Scanner sc = new Scanner(System.in);
   while (!sc.hasNextInt()) {
       sc.next(); // discard next token, which isn't a valid int
   }
   int nof = sc.nextInt();
for(i=0;i<nof;i++)
frame[i]= -1;

   int j=0;
   System.out.printf("\n");
   out.printf("\n");
for(i=0;i<pg;i++){
System.out.printf("%d\t",pages[i]);
out.printf("%d\t",pages[i]);
avail=0;
for(k=0;k<nof;k++)
if(frame[k]==pages[i])
avail=1;

  if (avail==0){
frame[j]=pages[i];
j=(j+1) % nof;
count++;

for(k=0;k<nof;k++)
if(frame[k]!=-1){
System.out.printf("%d",frame[k]);
out.printf("%d",frame[k]);
}
   
System.out.printf("-->F");
out.printf("-->F");
     }

     if(avail==1){
   for(k=0;k<nof;k++)
    if(frame[k]!=-1){
    System.out.printf("%d",frame[k]);
    out.printf("%d",frame[k]);
    }
     }
     System.out.printf("\n");
     out.printf("\n");
}
System.out.printf("\nNo of Faults: %d",count);
out.printf("\nNo of Faults: %d",count);
out.close();
write.close();
}
/**
* Lets the user select an input file using a standard file
* selection dialog box. If the user cancels the dialog
* without selecting a file, the return value is null.
*/
static File getInputFileNameFromUser() {
JFileChooser fileDialog = new JFileChooser();
fileDialog.setDialogTitle("Select File for Input");
int option = fileDialog.showOpenDialog(null);
if (option != JFileChooser.APPROVE_OPTION)
return null;
else
return fileDialog.getSelectedFile();
}//end of choosing file

}

©Dixit Bhatta 2013