Java.util.PriorityQueue class in Java
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 : ------
// Java Program illustrating the methods // of java.utl.priorityQueue class // add(), comparator(), conatins(), iterator(), offer() // peek(), poll(), toArray(), size(), toArray(t[] g1), // remove(), clear() import java.util.*; public class NewClass { public static void main(String[] args) { // Creating a Priority Queue : PriorityQueue <Integer> geek = new PriorityQueue <Integer> (); for ( int i= 2 ; i<= 20 ; i=i+ 2 ) { // Use of add() : geek.add( new Integer (i)); } System.out.println( "geek PriorityQueue : " + geek); // Use of comparator() // No ordering is required here as it is naturally ordered. Comparator geek_comp = geek.comparator(); System.out.println( "geek PriorityQueue : " + geek_comp); // Use of contains() boolean check = geek.contains( 6 ); System.out.println( "Use of contains() : " + check); // Use of iterator() Iterator g_iterator = geek.iterator(); System.out.print( "Iterator values : " ); while (g_iterator.hasNext()) { System.out.print(g_iterator.next() + " " ); } System.out.println( "" ); // Use of offer() geek.offer( 3050 ); System.out.println( "geek PriorityQueue : " + geek); // Use of peek() System.out.println( "Head of PriorityQueue via peek : " + geek.peek()); //Use of poll() int h = geek.poll(); System.out.println( "\nHead of PriorityQueue via poll : " + h); System.out.println( "geek PriorityQueue bcz of poll() : " + geek); // Use of remove() boolean r = geek.remove( 8 ); System.out.println( "\nCan remove : " + r); System.out.println( "geek PriorityQueue bcz of remove() : " + geek); // use of size() System.out.println( "\nSize of PriorityQueue : " + geek.size()); // Use of toArray() 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" ); // Use of toArray(t[] g1) : 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" ); // Use of clear() 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() : []