getting random results in priority queue

[somjit{}]

i wrote a code to implement some basics of priority queue , but apparantly its not giving desired output. the code is implemented using binary heap as its data structure. i tried tinkering here and there , nut no luck... i want to display a given number of max or min items, but im just getting a random selection of words from the file as output. any help with the code will be great. :)

this is my priority queue code:

public class MaxPQ<Key extends Comparable<Key>> {

    private Key[] pq;
    private int N;

    // create an empty priroty queue
    @SuppressWarnings("unchecked")
    public MaxPQ(int capacity){

        pq = (Key[])new Comparable[capacity+1];
    }

    //insert a key into a priority queue
    public void insert(Key v){
        pq[++N] = v;
        swim(N);
    }

    public int size(){
        return N;
    }

    // delete the max key   
    public Key delMax(){
        Key max = pq[1];
        exch(1,N--);
        sink(1);
        pq[N+1] = null;
        return max;
    }
    public Key delMin(){
        Key min = pq[N--];
        pq[N+1] = null;
        return min;
    }

    // is the priority queue empty  
    public boolean isEmpty(){
        return N == 0;
    }
    private void swim(int k){
        while(k>1 && less(k/2,k)){
            exch(k,k/2);
            k = k/2;
        }
    }
    private void sink(int k){
        while(2*k <= N){
            int j = 2*k;
            if( j < N && less(j,j+1)) j++;
            if(!less(k,j)) break;
            exch(k,j);
            k=j;
        }
    }
    private boolean less(int i,int j){
        return pq[i].compareTo(pq[j]) < 0;
    }
    private void exch(int i , int j){
        Key temp = pq[i];
        pq[i] = pq[j];
        pq[j] = temp;
    }
    public void displayItems(){
        for(Key i : pq)
            System.out.println(" " + i);
    }

}

this is the tester method

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.io.IOException;

public class testerPQ {

    public static void main(String[] args) throws FileNotFoundException{
        MaxPQ<String> pq = new MaxPQ<String>(3);
        BufferedReader is = new BufferedReader(new FileReader("C:/Documents and Settings/Somjit/Desktop/pqtest.txt"));
        String Line;
        try {
            while((Line = is.readLine()) != null){
                    pq.insert(Line);
                    if(pq.size() > 2)
                        pq.delMin();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        pq.displayItems();
        System.out.println("finished executing");

    }

}

and this is the file from which the code is reading :

a
hi
cat
lion
tiger
monkey
dinosaur
hippopotamus
jurrasicparkthree
kjhkjhkjhkjhkjhkjhh