how to sort the elements of a PriorityQueue using comparator in collections in java
how to sort the elements of a PriorityQueue using comparator in collections in java
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In this example we shall see how to sort the elements of a PriorityQueue using comparator class.
For creating a PriorityQueue first of all we have to import the java.util package in which the java.util.PriorityQueue class is defined. In this example we have created a class named CollectionsExample in which we created an object of the PriorityQueue and added some elements to the queue.
In this example we have implemented the compare(Object obj1, Object obj2) method of the comparator interface. In this example we have created an anonymous class in which we have defined our comparator which sorts the values of the queue in the descending order. For sorting the elements we have used the compareTo(Object obj1, Object obj2) of the comparable interface. This method returns a negative, zero or positive integer depensing on whether the first object is less than, equal to, or greater than the second.
We have also used the add(Object obj) method for adding the elements to the PriorityQueue.
In this example we have created a class named CollectionsExample in which we have created an object of the PriorityQueue pq , we have also created an anonymous class during its object intializaton and implemented the comparable interface's compareTo() method for sorting the values of the queue.
To the PriorityQueue, we have used the add(Object obj) method for adding the objects to the queue. Then, finally we have invoked the iterator() method on the object of the PriorityQueue pq and displayed its contents.
package r4r.co.in;
import java.util.*;
public class CollectionsExample {
/**
* @param args
*/
public static void main(String[] args) throws NullPointerException, ClassCastException
{
// TODO Auto-generated method stub
try
{
/* This code creates a PriorityQueue object by invoking constructor PriorityQueue(int capacity, Comparator obj)
* Also we have created an anonymous class which implements the comparable Interface and also its methods
*/
PriorityQueue<Integer> pq=new PriorityQueue<Integer>(12, new Comparator<Integer>()
{
public int compare(Integer num1, Integer num2)
{
Integer inum1, inum2;
inum1=num1;
inum2=num2;
if(inum1.compareTo(inum2)<1)
{
return 1;
}
else
{
return -1;
}
}
});
pq.add(3); // adding some random values to priorityqueue pq
pq.add(4);
pq.add(5);
pq.add(6);
pq.add(1);
Iterator<Integer> itr=pq.iterator(); //invoking the iterator over the pq
System.out.println("The elements in the priority queue are: ");
while(itr.hasNext())
{
System.out.println(itr.next()); // displaying the elements of the queue
}
}
catch(NullPointerException e)
{
e.printStackTrace();
}
catch(ClassCastException e)
{
e.printStackTrace();
}
}
}
The output of the above example is shown as:
The elements in the priority queue are:
6
5
4
3
1
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