Java.util.PriorityQueue class in Java (original) (raw)
Last Updated : 06 Dec, 2021
It is a priority queue based on priority heap.
- Elements in this class are in natural order or depends on the Constructor we used at this the time of construction.
- It doesn’t permit null pointers.
- It doesn’t allow inserting a non-comparable object, if it relies on natural ordering.
Constructors:
- PriorityQueue(): Creates a PriorityQueue with the default initial capacity (11) that orders its elements according to their natural ordering.
- PriorityQueue(Collection c): Creates a PriorityQueue containing the elements in the specified collection.
- PriorityQueue(int initialCapacity): Creates a PriorityQueue with the specified initial capacity that orders its elements according to their natural ordering.
- PriorityQueue(int initialCapacity, Comparator comparator): Creates a PriorityQueue with the specified initial capacity that orders its elements according to the specified comparator.
- PriorityQueue(PriorityQueue c): Creates a PriorityQueue containing the elements in the specified priority queue.
- PriorityQueue(SortedSet c): Creates a PriorityQueue containing the elements in the specified sorted set.
Declaration :
public class PriorityQueue extends AbstractQueue implements Serializable
Methods:
- add(element) : java.util.PriorityQueue.add() insert the elements to the Priority Queue.
Syntax :
public boolean add(E e)
Parameters :
element : the element we need to add.
Return :
call return true.
Exception :
-> ClassCastException
-> NullPointerException - comparator() : java.util.PriorityQueue.comparator() orders the elements in the queue.
Syntax :
public Comparator comparator()
Parameters :
Return :
orders the queue or return null, if it is naturally ordered
Exception :
- contains(Object obj) : java.util.PriorityQueue.contains(obj) returns true if the priority queue contains the element “obj”.
Syntax :
public boolean contains(Object obj)
Parameters :
obj : object to be checked
Return :
true - if the object is present else, return false
Exception : - iterator() : java.util.PriorityQueue.iterator() iterates over the queue element.
Syntax :
public Iterator iterator()
Parameters :
Return :
calls iterator over the elements in the queue.
Exception :
- offer(element) : java.util.PriorityQueue.offer() is required to insert a specific element to the given priority queue.
Syntax :
public boolean offer(E element)
Parameters :
element : specific element to be entered.
Return :
call return true.
Exception :
-> ClassCastException
-> NullPointerException - peek() : java.util.PriorityQueue.peek() identifies the head element of the queue.
Syntax :
public E peek()
Parameters :
Return :
calls if head exists, else null
Exception :
- poll() : java.util.PriorityQueue.poll() identifies the head and then removes it.
Syntax :
public E poll()
Parameters :
Return :
calls if head exists, else null
Exception :
- remove(Object obj) : java.util.PriorityQueue.remove() removes a specific object from the queue.
Syntax :
public boolean remove(Object obj)
Parameters :
obj : object to be removed
Return :
true - if obj is removed
Exception :
- size() : java.util.PriorityQueue.size() returns the size of elements in the Priority Queue.
Syntax :
public int size()
Parameters :
Return :
no. of elements
Exception :
- toArray() : java.util.PriorityQueue.toArray() returns an array containing the elements of PriorityQueue.
Syntax :
public Object[] toArray()
Parameters :
Return :
returns an array containing all the elements of PriorityQueue.
Exception :
- toArray(T[] array) : java.util.PriorityQueue.toArray(T[] a) returns the array having the elements of the Priority Queue.
Syntax :
public T[] toArray(T[] array)
Parameters :
array : the array to which are to be sorted.
Return :
call an array containing all the elements of the array.
Exception :
-> ArrayStoreException
-> NullPointerException - clear() : java.util.PriorityQueue.clear() clears all the elements of the PriorityQueue.
Syntax :
public void clear()
Parameters :
Return :
Exception :
import java.util.*;
public class NewClass
{
`` public static void main(String[] args)
`` {
`` PriorityQueue <Integer> geek = new PriorityQueue <Integer> ();
`` for ( int i= 2 ; i<= 20 ; i=i+ 2 )
`` {
`` geek.add( new Integer (i));
`` }
`` System.out.println( "geek PriorityQueue : " + geek);
`` Comparator geek_comp = geek.comparator();
`` System.out.println( "geek PriorityQueue : " + geek_comp);
`` boolean check = geek.contains( 6 );
`` System.out.println( "Use of contains() : " + check);
`` Iterator g_iterator = geek.iterator();
`` System.out.print( "Iterator values : " );
`` while (g_iterator.hasNext())
`` {
`` System.out.print(g_iterator.next() + " " );
`` }
`` System.out.println( "" );
`` geek.offer( 3050 );
`` System.out.println( "geek PriorityQueue : " + geek);
`` System.out.println( "Head of PriorityQueue via peek : " + geek.peek());
`` int h = geek.poll();
`` System.out.println( "\nHead of PriorityQueue via poll : " + h);
`` System.out.println( "geek PriorityQueue bcz of poll() : " + geek);
`` boolean r = geek.remove( 8 );
`` System.out.println( "\nCan remove : " + r);
`` System.out.println( "geek PriorityQueue bcz of remove() : " + geek);
`` System.out.println( "\nSize of PriorityQueue : " + geek.size());
`` Object[] g = geek.toArray();
`` System.out.print ( "Array from PriorityQueue : " );
`` for ( int i = 0 ; i<g.length; i++ )
`` {
`` System.out.print (g[i].toString() + " " ) ;
`` }
`` System.out.println( "\n" );
`` Integer[] g2 = new Integer[ 5 ];
`` Integer[] g1 = geek.toArray(g2);
`` System.out.print ( "Array from PriorityQueue of size 5 : " );
`` for ( int i = 0 ; i<g1.length; i++ )
`` {
`` System.out.print (g1[i].toString() + " " ) ;
`` }
`` System.out.println( "\n" );
`` geek.clear();
`` System.out.println( "PriorityQueue after clear() : " + geek);
`` }
}
Output :
geek PriorityQueue : [2, 4, 6, 8, 10, 12, 14, 16, 18, 20] geek PriorityQueue : null Use of contains() : true Iterator values : 2 4 6 8 10 12 14 16 18 20 geek PriorityQueue : [2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 3050] Head of PriorityQueue via peek : 2
Head of PriorityQueue via poll : 2 geek PriorityQueue bcz of poll() : [4, 8, 6, 16, 10, 12, 14, 3050, 18, 20]
Can remove : true geek PriorityQueue bcz of remove() : [4, 10, 6, 16, 20, 12, 14, 3050, 18]
Size of PriorityQueue : 9 Array from PriorityQueue : 4 10 6 16 20 12 14 3050 18
Array from PriorityQueue of size 5 : 4 10 6 16 20 12 14 3050 18
PriorityQueue after clear() : []