Semester 4 Operating System (OS) : Optimal page replacement policy Java program / Code

Given below is the Java Code for Optimal page replacement. //Aim:To implement optimal page replacement policy //Program: import java.util.*; class PR3 { static int check2(int p[],int pf[],int count[],int j,int s) {int k; for(int i=0;i<s;++i) count[i]=0; for(k=0;k<s;++k) { loop:for(int i=j-1;;--i) { ++count[k]; if(p[i]==pf[k]) break loop; } //System.out.println("count = "+count[k]); } int max=count[0]; int pos=0; for(int l=0;l<s;++l) { if(count[l]>max) { max=count[l]; pos=l; } } return pos; } static int check(int p[],int pf[],int count[],int j,int s) { int k; for(int i=0;i<s;++i) count[i]=0;int found=0; for(k=0;k<s;++k) { loop:for(int i=j+1;i<p.length;++i) { ++count[k]; if(p[i]==pf[k]) { ++found; break loop; } } } int pos; if(found<(s-1)) { System.out.println(); System.out.println("More than 1 used pages not required for furthur operation.\nSwapping LRU page."); pos=check2(p,pf,count,j,s); } else { int max=count[0]; pos=0; for(int l=0;l<s;++l) { if(count[l]>max) { max=count[l]; pos=l; } } } return pos; } static boolean check1(int p[],int x,int n) { for(int i=0;i<n;++i) { if(p[i]==x) return true; } return false; } public static void main(String args[]) { Scanner scr=new Scanner(System.in); System.out.println("Enter the number of page entries"); int n=scr.nextInt(); int fault=0,hit=0; int p[]=new int[n]; System.out.println("Enter the pages "); for(int i=0;i<n;++i) p[i]=scr.nextInt(); System.out.print("The page table entries are "); for(int i=0;i<n;++i) System.out.print(" "+p[i]); System.out.println(); int s=3; System.out.println("Do you wish to set a the number of page frames?(1=yes/0=no)"); int ch=scr.nextInt(); if(ch==1) { System.out.println("Enter the number of page frames "); s=scr.nextInt(); System.out.println("The number of page frames set to "+s); } else System.out.println("The default number of page frames are "+s); int count[]=new int[s]; int pf[]=new int[s]; int t=0; int incr=0; for(int i=0;i<s || (t!=s);++i) { if(check1(pf,p[i],t)) { ++incr; System.out.println(); for(int y=0;y<t;++y) System.out.print(pf[y]+" "); System.out.print(" Hit"); ++hit; } else {++incr; ++t; pf[t-1]=p[i]; System.out.println(); for(int y=0;y<t;++y) System.out.print(pf[y]+" "); System.out.print(" F"); ++fault; } } for(int j=incr;j<n;++j) { if(check1(pf,p[j],s)) { ++hit; System.out.println(); for(int k=0;k<s;++k) System.out.print(pf[k]+" "); System.out.print(" H"); } else { int choice=check(p,pf,count,j,s); ++fault; pf[choice]=p[j]; System.out.println(); for(int k=0;k<s;++k) System.out.print(pf[k]+" "); System.out.print(" F"); } } System.out.println(); System.out.println("Page faults= "+fault+" Page hits= "+hit); } } /* OUTPUT Enter the number of page entries 20 Enter the pages 7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1 The page table entries are 7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1 Do you wish to set a the number of page frames?(1=yes/0=no) 0 The default number of page frames are 3 7 F 7 0 F 7 0 1 F 2 0 1 F 2 0 1 H 2 0 3 F 2 0 3 H 2 4 3 F 2 4 3 H 2 4 3 H 2 0 3 F 2 0 3 H 2 0 3 H 2 0 1 F 2 0 1 H 2 0 1 H 2 0 1 H 7 0 1 F 7 0 1 H 7 0 1 H Page faults= 9 Page hits= 11 Enter the number of page entries 20 Enter the pages 7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1 The page table entries are 7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1 Do you wish to set a the number of page frames?(1=yes/0=no) 1 Enter the number of page frames 4 The number of page frames set to 4 7 F 7 0 F 7 0 1 F 7 0 1 2 F 7 0 1 2 H 3 0 1 2 F 3 0 1 2 H 3 0 4 2 F 3 0 4 2 H 3 0 4 2 H 3 0 4 2 H 3 0 4 2 H 3 0 4 2 H 1 0 4 2 F 1 0 4 2 H 1 0 4 2 H 1 0 4 2 H 7 0 4 2 F 7 0 4 2 H 1 0 4 2 F Page faults= 9 Page hits= 11 */