Least Recently Used (LRU) Page Replacement Algorithm > Java Program

Computer Organization and Architecture

Least Recently Used (LRU) Page Replacement Algorithm > Java Program

In Least Recently Used (LRU) page replacement algorithm we use the recent past as an approximation of the near future,then we will replace the pagethat has not been used for the longest period of time. In Least Recently Used (LRU) page replacement algorithm is associated with the each page the time of that page's last use.When a page must be replaced,In Least Recently Used (LRU) page replacement algorithm chooses that page has not been used for longest period of time.The In Least Recently Used (LRU) page replacement algorithm Policy is often used as page replacement algorithm and is consider to be good.The major problem is how to implement In Least Recently Used (LRU) page replacement algorithm.An In Least Recently Used (LRU) page replacement algorithm may require substantial hardware assistance. 

import java.util.*;
class LRU
{
public static void main(String args[])
{
Scanner sc=new Scanner(System.in);

System.out.println("ENTER NUMBER OF FRAMES");
int nf=sc.nextInt();
System.out.println("ENTER NUMBER OF REFERENCES");
int nr=sc.nextInt();
int page[]=new int[nr];
int frame[]=new int[nr];
                System.out.println("ENTER REFERENCE");
for(int i=0;i<nr;i++)
page[i]=sc.nextInt();
for(int i=0;i<nf;i++)
frame[i]=-1;
for(int k=0;k<nf;k++)
System.out.print(" "+frame[k]);
System.out.println();
int flag=0,hit=0,miss=0,front=0,rear=-1;
int age[]=new int[nf];
for(int i=0;i<nf;i++)
age[i]=0;
for(int j=0,i=0;j<nf && i<nr;j=j%nf,i++)
{
flag=0;

for(int y=0;y<nf;y++)
{
if(frame[y]==page[i])
{
flag=1;
hit++;
age[y]=0;
}
}
if(flag==0)
if(frame[j]==-1)
{

frame[j]=page[i];
                                        miss++;
rear++;
j++;
}
else

{
int max=age[0],loc=0;
miss++;


for(int b=0;b<nf;b++)
if(age[b]>max)
{
max=age[b];loc=b;
}
frame[loc]=page[i];
age[loc]=0;
j++;
                                        }
for(int k=0;k<nf;k++)
System.out.print(" "+frame[k]);
System.out.println();
for(int a=0;a<nf;a++)
{
if(frame[a]==-1)
age[a]=0;
else
age[a]++;
}

/*for(int k=0;k<nf;k++)
System.out.print(" "+age[k]);
System.out.println();*/
}
float hr=(float)hit/((float)hit+(float)miss);
System.out.println("Hit="+hit+" miss="+miss);
System.out.println("page replacement ratio="+hr);
}
}

/*
run:
ENTER NUMBER OF FRAMES
3
ENTER NUMBER OF REFERENCES
12
ENTER REFERENCE
1
2
3
4
1
2
5
1
2
3
4
5
 -1 -1 -1
 1 -1 -1
 1 2 -1
 1 2 3
 4 2 3
 4 1 3
 4 1 2
 5 1 2
 5 1 2
 5 1 2
 3 1 2
 3 4 2
 3 4 5
Hit=2 miss=10
page replacement ratio=0.16666667
BUILD SUCCESSFUL (total time: 23 seconds)

*/