Java PriorityQueue iterator() Method

Description

The Java PriorityQueue iterator() method returns an iterator over the elements in this queue. This iterator then can be used to iterate each element of the PriorityQueue object.

Declaration

Following is the declaration for java.util.PriorityQueue.iterator() method

public Iterator<E> iterator()

Parameters

NA

Return Value

This method returns an iterator over the elements in this queue.

Exception

NA

Iterating PriorityQueue of Ints using iterator() Method Example

The following example shows the usage of Java PriorityQueue iterator() method to iterate Integers. We're adding couple of Integers to the PriorityQueue object using add() method calls per element and then iterate and print each element to show the elements added.

package com.tutorialspoint;

import java.util.PriorityQueue;

import java.util.Iterator;

public class PriorityQueueDemo {
   public static void main(String[] args) {
      
      // create an empty priority queue
      PriorityQueue<Integer> queue = new PriorityQueue<>();

      // use add() method to add elements in the queue
      queue.add(15);
      queue.add(22);
      queue.add(25);
      queue.add(20);

      // iterator() is used to print all the elements
      // next() returns the next element on each iteration
      System.out.println("printing elements using iterator:");
      for(Iterator<Integer> itr = queue.iterator();itr.hasNext();)  {
         System.out.println(itr.next());
      }
   }
}   

Output

Let us compile and run the above program, this will produce the following result −

printing elements using iterator:
15
20
25
22

Iterating PriorityQueue of Strings using iterator() Method Example

The following example shows the usage of Java PriorityQueue iterator() method to iterate Strings. We're adding couple of Strings to the PriorityQueue object using add() method calls per element and then iterate and print each element to show the elements added.

package com.tutorialspoint;

import java.util.PriorityQueue;

import java.util.Iterator;

public class PriorityQueueDemo {
   public static void main(String[] args) {
      
      // create an empty priority queue
      PriorityQueue<String> queue = new PriorityQueue<>();

      // use add() method to add elements in the queue
      queue.add("A");
      queue.add("B");
      queue.add("C");
      queue.add("D");

      // iterator() is used to print all the elements
      // next() returns the next element on each iteration
      System.out.println("printing elements using iterator:");
      for(Iterator<String> itr = queue.iterator();itr.hasNext();)  {
         System.out.println(itr.next());
      }
   }
}   

Output

Let us compile and run the above program, this will produce the following result −

printing elements using iterator:
A
B
C
D

Iterating PriorityQueue of Objects using iterator() method Example

The following example shows the usage of Java PriorityQueue iterator() method to iterate Student objects. We're adding couple of Student objects to the PriorityQueue object using add() method calls per element and then iterate and print each element to show the elements added.

package com.tutorialspoint;

import java.util.PriorityQueue;

import java.util.Iterator;

public class PriorityQueueDemo {
   public static void main(String[] args) {
      
      // create an empty priority queue
      PriorityQueue<Student> queue = new PriorityQueue<>();

      // use add() method to add elements in the queue
      queue.add(new Student(1, "Julie"));
      queue.add(new Student(2, "Robert"));
      queue.add(new Student(3, "Adam"));

      // iterator() is used to print all the elements
      // next() returns the next element on each iteration
      System.out.println("printing elements using iterator:");
      for(Iterator<Student> itr = queue.iterator();itr.hasNext();)  {
         System.out.println(itr.next());
      }
   }
}
class Student implements Comparable<Student> {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
   
   @Override
   public boolean equals(Object obj) {
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }

   @Override
   public int compareTo(Student student) {
      return this.rollNo - student.rollNo;
   }
} 

Output

Let us compile and run the above program, this will produce the following result −

printing elements using iterator:
[ 1, Julie ]
[ 2, Robert ]
[ 3, Adam ]