This Java program Implements PriorityQueue API.An unbounded priority queue based on a priority heap. 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. A priority queue does not permit null elements. A priority queue relying on natural ordering also does not permit insertion of non-comparable objects (doing so may result in ClassCastException).
Here is the source code of the Java Program to Implement PriorityQueue. The Java program is successfully compiled and run on a Linux system. The program output is also shown below.
import java.util.Collection; import java.util.Comparator; import java.util.Iterator; import java.util.PriorityQueue; public class PriorityQueueImpl<E> { private PriorityQueue<E> priorityQueue; /** * Creates a PriorityQueue with the default initial capacity (11) that * orders its elements according to their natural ordering. **/ public PriorityQueueImpl() { priorityQueue = new PriorityQueue<E>(); } /** * Creates a PriorityQueue containing the elements in the specified * collection. **/ public PriorityQueueImpl(Collection<? extends E> c) { priorityQueue = new PriorityQueue<E>(c); } /** * Creates a PriorityQueue with the specified initial capacity that orders * its elements according to their natural ordering. **/ public PriorityQueueImpl(int initialCapacity) { priorityQueue = new PriorityQueue<E>(initialCapacity); } /** * Creates a PriorityQueue with the specified initial capacity that orders * its elements according to the specified comparator. **/ public PriorityQueueImpl(int initialCapacity, Comparator<? super E> comparator) { priorityQueue = new PriorityQueue<E>(initialCapacity, comparator); } /** Inserts the specified element at the tail of this queue. **/ public boolean add(E e) { return priorityQueue.add(e); } /** Atomically removes all of the elements from this queue. **/ public void clear() { priorityQueue.clear(); } /** Returns true if this queue contains the specified element. **/ public boolean contains(Object o) { return priorityQueue.contains(o); } /** Returns an iterator over the elements in this queue in proper sequence. **/ public Iterator<E> iterator() { return priorityQueue.iterator(); } /** * Inserts the specified element at the tail of this queue if it is possible * to do so immediately without exceeding the queue's capacity, returning * true upon success and false if this queue is full. **/ public boolean offer(E e) { return priorityQueue.offer(e); } /** * Retrieves, but does not remove, the head of this queue, or returns null * if this queue is empty. **/ public E peek() { return priorityQueue.peek(); } /** * Retrieves and removes the head of this queue, or returns null if this * queue is empty. **/ public E poll() { return priorityQueue.poll(); } /** * Removes a single instance of the specified element from this queue, if it * is present. **/ public boolean remove(Object o) { return priorityQueue.remove(o); } /** Returns the number of elements in this queue. **/ public int size() { return priorityQueue.size(); } /** * Returns an array containing all of the elements in this queue, in proper * sequence. **/ public Object[] toArray() { return priorityQueue.toArray(); } /** * Returns an array containing all of the elements in this queue, in proper * sequence; the runtime type of the returned array is that of the specified * array. **/ public <T> T[] toArray(T[] a) { return priorityQueue.toArray(a); } public static void main(String... arg) { PriorityQueueImpl<Integer> priorityQueue = new PriorityQueueImpl<Integer>(); priorityQueue.add(200); priorityQueue.add(49); priorityQueue.add(-400); priorityQueue.add(240); priorityQueue.add(0); System.out.println("the elements of the priorityQueue is "); Iterator<Integer> itr = priorityQueue.iterator(); while (itr.hasNext()) { System.out.print(itr.next() + "\t"); } System.out.println(); priorityQueue.offer(600); priorityQueue.offer(700); System.out.println("the peak element of the priorityQueue is(by peeking) " + priorityQueue.peek()); System.out.println("the peak element of the priorityQueue is(by polling) " + priorityQueue.poll()); System.out.println("element 300 removed " + priorityQueue.remove(300)); System.out.println("the priorityQueue contains 400 :" + priorityQueue.contains(400)); System.out.println("the priorityQueue contains 100 :" + priorityQueue.contains(200)); System.out.println("the size of the priorityQueue is " + priorityQueue.size()); } }
$ javac PriorityQueueImpl.java $ java PriorityQueueImpl the elements of the priorityQueue is -400 0 49 240 200 the peak element of the priorityQueue is(by peeking) -400 the peak element of the priorityQueue is(by polling) -400 element 300 removed false the priorityQueue contains 400 :false the priorityQueue contains 100 :true the size of the priorityQueue is 6
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