priority queue!

[vijay umar]

here is one code:

import java.util.*;
class PQ
{
static class PQsort
implements Comparator<Integer> {

public int compare(Integer one, Integer two) {
return two - one; // unboxing
}
}
public static void main(String[] args)
{
int[] ia = {1,5,3,7,6,9,8 }; // unordered data
PriorityQueue<Integer> pq1 = new PriorityQueue<Integer>(); // use natural order
for(int x : ia) // load queue
pq1.offer(x);
for(int x : ia)
System.out.print(pq1.poll() + " ");
System.out.println("");
PQsort pqs = new PQsort(); // get a Comparator
PriorityQueue<Integer> pq2 = new PriorityQueue<Integer>(10,pqs); // use Comparator
for(int x : ia) // load queue
pq2.offer(x);
System.out.println("size " + pq2.size());
System.out.println("peek " + pq2.peek());
System.out.println("size " + pq2.size());
System.out.println("poll " + pq2.poll());
System.out.println("size " + pq2.size());
for(int x : ia) // review queue
System.out.print(pq2.poll() + " ");
}
}

in this code i dint understand that how the comparator is working.How does it arrange the elements in the queue?
espicially this one:
[b]implements Comparator<Integer> {

public int compare(Integer one, Integer two) {
return two - one; // unboxing
}
how does this works?please explain!

[armando fonseca]

hi vijay,
look this part carefully,

public int compare(Integer one, Integer two) {
   return two - one; // unboxing
} 

You are comparing two numbers by subtracting them!
if integer two > than integer one
then it return a positive number , zero if they are equal and a negative number if integer two is less than integer one. Using your code , it will order from highest to lowest if I'm not mistaken( I'm not sure!.... any the order is irrelevant). Then when you are adding the numbers at:

pq2.offer(x);

, it will use the sorting algorithm to store the values in the queue rather than using FIFO.
Now I have a question to you vijay, by looking your comparator implementation, is the output: 9,8,7,6,5,3,1 when traversing ?

-Armando

[Ankit Garg]

import java.util.*;
class PQ
{
   static class PQsort
   implements Comparator<Integer> {
      public int compare(Integer one, Integer two) {
         return two - one; // unboxing
     }
   }
   public static void main(String[] args)
   {
      int[] ia = {1,5,3,7,6,9,8 }; // unordered data
      PriorityQueue<Integer> pq1 = new PriorityQueue<Integer>(); // use natural order
      for(int x : ia) // load queue
         pq1.offer(x);
      for(int x : ia)
         System.out.print(pq1.poll() + " ");
      System.out.println("");
      PQsort pqs = new PQsort(); // get a Comparator
      PriorityQueue<Integer> pq2 = new PriorityQueue<Integer>(10,pqs); // use Comparator
      for(int x : ia) // load queue
         pq2.offer(x);
      System.out.println("size " + pq2.size());
      System.out.println("peek " + pq2.peek());
      System.out.println("size " + pq2.size());
      System.out.println("poll " + pq2.poll());
      System.out.println("size " + pq2.size());
      for(int x : ia) // review queue
         System.out.print(pq2.poll() + " ");
   }
} 

Please Use Code Tags to make your code readable...

[Shin Kudo]

He wants to make the code look like in real SCJP exam

[Ankit Garg]

Shin Kudo wrote:He wants to make the code look like in real SCJP exam

In the real SCJP exam, the code has proper indentation. It's just that the code is jammed into the smallest size possible. So this code would come something like this

import java.util.*;
class PQ{
   static class PQsort  implements Comparator<Integer> {
      public int compare(Integer one, Integer two) { return two - one; }
   }
   public static void main(String[] args){
      int[] ia = {1,5,3,7,6,9,8 };
      PriorityQueue<Integer> pq1 = new PriorityQueue<Integer>();
      for(int x : ia){ pq1.offer(x); }
      for(int x : ia){ System.out.print(pq1.poll() + " "); }
      System.out.println("");
      PQsort pqs = new PQsort();
      PriorityQueue<Integer> pq2 = new PriorityQueue<Integer>(10,pqs);
      for(int x : ia){ pq2.offer(x); }
      System.out.println("size " + pq2.size());
      System.out.println("peek " + pq2.peek());
      System.out.println("size " + pq2.size());
      System.out.println("poll " + pq2.poll());
      System.out.println("size " + pq2.size());
      for(int x : ia) { System.out.print(pq2.poll() + " "); }
   }
} 

[vijay umar]

hi armando ,

nice meeting you

thanks for replying


yes the queue is sorted like that.