Java TreeSet descendingIterator() Method

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Description

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

Declaration

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

public Iterator<E> descendingIterator()

Parameters

NA

Return Value

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

Exception

NA

Getting DescendingIterator of a TreeSet of Integer Example

The following example shows the usage of Java TreeSet descendingIterator() method to get an iterator over the elements in this set in descending order. We've created a TreeSet object of Integer. Then few entries are added using add() method. Using descendingIterator(), we've received an iterator and iterated trough its value.

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 descending iterator
      Iterator iterator;
      iterator = treeset.descendingIterator();

      // displaying the Tree set data
      System.out.println("Tree set data in descending 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 descending order: 
17 
13 
2 
1 

Getting DescendingIterator of a TreeSet of String Example

The following example shows the usage of Java TreeSet descendingIterator() method to get an iterator over the elements in this set in descending order. We've created a TreeSet object of String. Then few entries are added using add() method. Using descendingIterator(), we've received an iterator and iterated trough its value.

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("A");
      treeset.add("C");
      treeset.add("B");
      treeset.add("D");

      // create descending iterator
      Iterator iterator;
      iterator = treeset.descendingIterator();

      // displaying the Tree set data
      System.out.println("Tree set data in descending 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 descending order: 
D 
C 
B 
A 

Getting DescendingIterator of a TreeSet of Object Example

The following example shows the usage of Java TreeSet descendingIterator() method to get an iterator over the elements in this set in descending order. We've created a TreeSet object of Student objects. Then few entries are added using add() method. Using descendingIterator(), we've received an iterator and iterated trough its value.

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(2, "Julie")); 
      treeset.add(new Student(4, "Julia"));
      treeset.add(new Student(3, "Adam"));
      treeset.add(new Student(1, "Robert"));
      // create descending iterator
      Iterator iterator;
      iterator = treeset.descendingIterator();

      // displaying the Tree set data
      System.out.println("Tree set data in descending 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 descending order: 
[ 4, Julia ] 
[ 3, Adam ] 
[ 2, Julie ] 
[ 1, Robert ]