Here is a simulation of Optimal Page replacement algorithm in operating system . . .Suggestions to improve the simulation are welcome :-)

Optimal.java

import java.util.Scanner;

public class Optimal

{

public static void main(String[] args)

{

System.out.println("Enter the number of Frames");

Scanner sc = new Scanner(System.in);

int F = sc.nextInt();

Page page[] = new Page[F];

for(int i=0;i<F;i++)

{

page[i] = new Page();

}

int pages[] = new int[100];

System.out.println("Enter the String References : (0 for Exit)");

int size =0;

while(true)

{

int x = sc.nextInt();

if(x==0) 

break;

pages[size++] = x;

}

// Now we check for page Fault

for(int j=0;j<size;j++)

{

boolean pageFaultOccured=true;

for(int k=0;k<F;k++)

{

if(page[k].pno == pages[j])

{

// No Page Fault

pageFaultOccured=false;

break;

}

}

if(pageFaultOccured == false)

{

System.out.println("NO PAGE FAULT :-)");

}

else

{

System.out.println("PAGE FAULT :-(");

// Check for Empty Frames and insert if any

boolean pageInserted=false;

for(int k=0;k<F;k++)

{

pageInserted=false;

if(page[k].pno == 0)

{

page[k].pno=pages[j];

System.out.println("Page Entered at Frame : "+k);

pageInserted=true;

break;

}

}

if(pageInserted==false)

{

int lf=0;

for(int k=0;k<F;k++)

{

if(page[lf].nextReferred(pages,j,size) < page[k].nextReferred(pages,j,size))

lf = k;

}

page[lf].pno = pages[j];

System.out.println("Page Entered at Frame : "+lf);

}

}

}

}

}

class Page

{

int pno;

Page()

{

this.pno = 0;

}

int nextReferred(int arr[], int curr, int size)

{

int next=0;

for(int i=curr; i<size; i++)

{

if(this.pno == arr[i])

{

next = i;

break;

}

}

if(next==0)

next=size+1;

return next;

}

}