Java TreeSet iterator() Method

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Description

The Java TreeSet iterator() method is used to return an iterator over the elements in this set in ascending order.

Declaration

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

public Iterator<E> iterator()

Parameters

NA

Return Value

The method call returns an iterator over the elements in this set in ascending order.

Exception

NA

Getting Iterator to Iterate a TreeSet of Integer Example

The following example shows the usage of Java TreeSet iterator() method to get a iterator of elements of the treeset. We've created a TreeSet object of Integer. Few entries are added using add() method and iterator is retrieved using iterator() method and then iterator is iterated to print the elements.

package com.tutorialspoint;

import java.util.Iterator;
import java.util.TreeSet;

public class TreeSetDemo {
   public static void main(String[] args) {

      // creating a TreeSet 
      TreeSet <Integer>treeset = new TreeSet<>();

      // adding in the tree set
      treeset.add(1);
      treeset.add(13);
      treeset.add(17);
      treeset.add(2);

      // create ascending iterator
      Iterator iterator;
      iterator = treeset.iterator();

      // displaying the Tree set data
      System.out.println("Tree set data in ascending order: ");     
      while (iterator.hasNext()) {
         System.out.println(iterator.next() + " ");
      }
   }     
}

Output

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

Tree set data in ascending order: 
1 
2 
13 
17 

Getting Iterator to Iterate a TreeSet of String Example

The following example shows the usage of Java TreeSet iterator() method to get a iterator of elements of the treeset. We've created a TreeSet object of String. Few entries are added using add() method and iterator is retrieved using iterator() method and then iterator is iterated to print the elements.

package com.tutorialspoint;

import java.util.Iterator;
import java.util.TreeSet;

public class TreeSetDemo {
   public static void main(String[] args) {

      // creating a TreeSet 
      TreeSet <String>treeset = new TreeSet<>();

      // adding in the tree set
      treeset.add("D");
      treeset.add("B");
      treeset.add("C");
      treeset.add("A");

      // create ascending iterator
      Iterator iterator;
      iterator = treeset.iterator();

      // displaying the Tree set data
      System.out.println("Tree set data in ascending order: ");     
      while (iterator.hasNext()) {
         System.out.println(iterator.next() + " ");
      }
   }     
}

Output

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

Tree set data in ascending order: 
A
B
C
D

Getting Iterator to Iterate a TreeSet of Object Example

The following example shows the usage of Java TreeSet iterator() method to get a iterator of elements of the treeset. We've created a TreeSet object of Student. Few entries are added using add() method and iterator is retrieved using iterator() method and then iterator is iterated to print the elements.

package com.tutorialspoint;

import java.util.Iterator;
import java.util.TreeSet;

public class TreeSetDemo {
   public static void main(String[] args) {

      // creating a TreeSet 
      TreeSet <Student>treeset = new TreeSet<>();

      // adding in the tree set
      treeset.add(new Student(1, "Robert"));
      treeset.add(new Student(3, "Adam"));
      treeset.add(new Student(2, "Julie"));
      treeset.add(new Student(4, "Julia"));

      // create ascending iterator
      Iterator iterator;
      iterator = treeset.iterator();

      // displaying the Tree set data
      System.out.println("Tree set data in ascending order: ");     
      while (iterator.hasNext()) {
         System.out.println(iterator.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.

Tree set data in ascending order: 
[ 1, Robert ] 
[ 2, Julie ] 
[ 3, Adam ] 
[ 4, Julia ]