LRU Simulation

Main.java

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Created by rohit on 2/1/16.
 * Program to implement LRU algorithm.
 * Min value priority : Indicates lease recently used.
 * Max value priority: Indicates recently used.
 *   I    Hit 2  Hit 1 Hit 3 Hit 2  Miss 6
 * |1 1| |1  0| |1 3| |1 2| |1 1|  |6 3|
 * |2 2| |2  3| |2 2| |2 1| |2 3|  |2 2|
 * |3 3| |3  2| |3 1| |3 3| |3 2|  |3 1|
 */

/*
 *Container for the page.
 */
class Frame{

    Page[] frame;
    int frameSize;
    //Hashmap which holds the prority for next insertion
    //key: the page data. value: position in the frame

    ConcurrentHashMap<Integer,Integer> priority;
    //Initiaze the page frame

    Frame(int size,Page[] pages){
      frame = new Page[size];
      frameSize = size;
      int cnt=0;
      priority = new ConcurrentHashMap<>();
      for(Page pg:pages){
          frame[cnt]=pg;
          priority.put(pg.data,cnt);
          cnt++;
      }
    }

    public void printPageFrame(){
        for(int i=0;i<frameSize;i++)
            System.out.println(frame[i].toString());
        System.out.println();
    }

    //Returns true if its a hit
    //Otherwise returns false implicitly indicating a miss
    public boolean isHit(Page page){
        for(Page currPage:frame){
            if(currPage.equals(page)){
                return true;
            }
        }
        return false;
    }

    public int findMaxPriority() {
        Set set = priority.keySet();
        Iterator itr = set.iterator();
        int max;
        max = priority.get(itr.next());
        while (itr.hasNext()) {
            int val = priority.get(itr.next());
            if (val > max)
                max = val;
        }
        return max;
    }

    public int findMinPriority() {
        Set set = priority.keySet();
        Iterator itr = set.iterator();
        int min;
        min = priority.get(itr.next());
        while (itr.hasNext()) {
            int val = priority.get(itr.next());
            if (val < min)
                min = val;
        }
        return min;
    }

    //No page frame change is desired as its a hit.
    //Page not found in the frame
    public void setMissPriority(Page page){
         //Find min in the set.
         int min = findMinPriority();
         int max = findMaxPriority();
         //At the hash key which has min put the max value
         Iterator itr1 = priority.keySet().iterator();
         while(itr1.hasNext()){
             Integer pg = (Integer)itr1.next();
             if(priority.get(pg)==min){
                 priority.put(page.data,max);
                 //Removed swapped out page of the frame
                 priority.remove(pg);
                 searchAndReplace(pg,page.data);
             }
         }
         //Reduce other priorities
         Iterator itr = priority.keySet().iterator();
         while(itr.hasNext()){
                 int value = (Integer)itr.next();
                 if(value != page.data){
                    int pri = priority.get(value);
                    priority.put(value,--pri);
                 }
         }
    }

    public void searchAndReplace(int x,int y){
        int i=0;
        for(i=0;i<frame.length;i++){
            if(frame[i].data == x)
                frame[i].data = y;
        }
    }

    //Page found in the frame
    public void setHitPriority(Page page){
        Set set = priority.keySet();
        //Find min in the value set.
        int min= findMaxPriority();
        priority.put(page.data,min);
        Iterator itr = priority.keySet().iterator();
        while(itr.hasNext()){
            int value = (Integer)itr.next();
            if(value!=page.data){
                int pri = priority.get(value);
                priority.put(value,--pri);
            }
        }
    }

    public boolean addPage(Page page){
        if(isHit(page)){
            setHitPriority(page);
            return true;
        }//Its a miss replace the page
        else{
            setMissPriority(page);
        }
        return false;
    }

    @Override
    public String toString() {
        StringBuffer buff = new StringBuffer();
        for(int i=0;i<frame.length;i++)
            buff.append(" "+frame[i].data+" ");
        return buff.toString();
    }
}
/*
 * Represents the Page which will sit int he frame.
 */
class Page{
    int data;
    Page(int data){
        this.data=data;
    }

    @Override
    public String toString() {
        return Integer.toString(data);
    }

    @Override
    public boolean equals(Object obj) {
        if(obj instanceof Page){
            Page page =(Page)obj;
            if(page.data == this.data)
                return true;
        }
       return false;
    }
}

public class Main {
   public static void main(String[] args){
     Frame frame = new Frame(3,new Page[]{new Page(10),new Page(20),new Page(30)});
     System.out.println(frame);
     frame.addPage(new Page(10));
     System.out.println(frame);
     frame.addPage(new Page(11));
     System.out.println(frame);
     frame.addPage(new Page(12));
     System.out.println(frame);
     frame.addPage(new Page(13));
     System.out.println(frame);
   }
}