How does Priority Queue work. This is my scenario, I have certain objects with priorities 1,2,..10. There could be multiple objects with same priority. I was thinking I can put them into a priority queue and let the pool() give me the objects with highest priority.. ?
I m kinda confused with PQ.
1) I get errors when i create a PQ <MyClass>.
2) Do i need to use comparator to ensure i check the priority of the object?
Pointers plz
Thanks
Pushkala
From the java doc.
>How does Priority Queue work.
The elements of the priority queue are ordered according to their natural ordering, or by a Comparator provided at queue construction time, depending on which constructor is used.
>I get errors when i create a PQ <MyClass>.
A priority queue relying on natural ordering also does not permit insertion of non-comparable objects.
Agreed. I inserted elements in PQ..
But things get weird.
1) Create a class called msg with variable "p"
2) I created PQ and Comparator to handle inserts of instances of msg and compare value of "p"
3) Now i insert more than one msg with same "p" (the various p values are 2,1,3,2)
4) For some reason, after i do all the "offers", when i print the pq,
the order i get is 1,2,3,2
5) Now if i do a peek() or pool(), then, the pq gets ordered and i get 1,2,2,3.
Any pointers..?
From the java doc.
>How does Priority Queue work.
The elements of the priority queue are ordered according to their natural ordering, or by a Comparator provided at queue construction time, depending on which constructor is used.
>I get errors when i create a PQ <MyClass>.
A priority queue relying on natural ordering also does not permit insertion of non-comparable objects.
public class Prioritizer implements Comparator<msgclass>
{
public int compare(msgclass o1, msgclass o2) {
int n = o2.getPriority()-o2.getPriority();
return n;
}
***************************************
class PQ {
public static void main(String[] args) {
msgclass a5 = new msgclass();
a5.setPriority(100);
msgclass a1 = new msgclass();
a1.setPriority(10);
msgclass a2 = new msgclass();
a2.setPriority(20);
msgclass a3 = new msgclass();
a3.setPriority(30);
msgclass a4 = new msgclass();
a4.setPriority(30);
msgclass a6 = new msgclass();
a6.setPriority(130);
Prioritizer pqs = new Prioritizer(); // get a Comparator
PriorityQueue<msgclass> pq2 =
new PriorityQueue<msgclass>(10,pqs); // use Comparator
pq2.add(a5);
pq2.add(a1);
pq2.add(a2);
pq2.add(a3);
pq2.add(a4);
pq2.add(a6);
System.out.println(pq2);
System.out.println("size " + pq2.size());
System.out.println("PEEK " + pq2.peek());
System.out.println("After PEEK"+pq2);
System.out.println("POOL " + pq2.poll());
System.out.println("After POLL"+pq2);
System.out.println("After POLL"+pq2);
}
}[(100), (10), (20), (30), (30), (130)]
size 6
PEEK (100)
After PEEK[(100), (10), (20), (30), (30), (130)]
POOL (100)
After POLL[(130), (10), (20), (30), (30)]
After POLL[(130), (10), (20), (30), (30)]
This is the output i get..
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