In this article, we will discuss TreeSet class – the implementation class for NavigableSet interface in detail

1. Key points about TreeSet:

• TreeSet doesn’t allow duplicate items
• maintains ascending sorting-order, by default

2. TreeSet:

• TreeSet is the implementation class of NavigableSet interface (i.e.; TreeSet implements NavigableSet)
• TreeSet uses balanced-tree to store element/objects
• Duplicate element/objects are NOT allowed
• If duplicate value is added again, then there won’t be any compile-time or runtime errors
• Simply add(object) method returns false for already containing object inside TreeSet
• At any time, TreeSet contains only unique element/objects
• Insertion-order is NOT maintained
• But TreeSet stores element/objects in sorting-order; it could be either default natural sorting order or programmer defined customized sorting-order
• Allows NULL insertion but maximum of only one NULL value (till Java 1.6 version)
• From Java 1.7 version, NULL insertion is not possible
• TreeSet is non-synchronized
• Present in java.util package and extends java.util.AbstractSet implements java.util.NavigableSet interface
• Also, implements java.lang.Cloneable, java.io.Serializable marker interfaces which provides special ability to TreeSet (provided by JVM at run time) like,
• java.lang.Cloneable: to create a duplicate object or to clone an object
• java.io.Serializable: to transfer objects across network

Source: Team BenchResources.Net

3. TreeSet constructors:

3.1 TreeSet ts = new TreeSet();

• creates an empty TreeSet object
• where elements will be inserted according to default natural sorting order

3.2 TreeSet ts = new TreeSet(Comparator c);

• creates an empty TreeSet object
• where elements will be inserted according to specified comparator object (i.e.; customized sorting order)

3.3 TreeSet ts = new TreeSet(Collection c);

• creates an equivalent TreeSet object for the specified collection
• it is basically used for inter-conversion between collection objects

3.4 TreeSet ts = new TreeSet(SortedSet s);

• create an equivalent TreeSet object for the specified SortedSet
• follows same ordering as per specified SortedSet

4. TreeSet examples:

TreeSetStringExample.java

package in.bench.resources.collection;

import java.util.TreeSet;

public class TreeSetStringExample  {

	public static void main(String[] args) {
		// creating TreeSet object of type String
		TreeSet<String> ts = new TreeSet<String>();

		// adding elements to TreeSet object
		ts.add("Sundar Pichai");
		ts.add("Satya Nadella");
		ts.add("Shiv Nadar");
		ts.add("Shantanu Narayen");
		ts.add("Sundar Pichai"); // adding duplicate element
		ts.add("Francisco D’Souza");
		ts.add("Vishal Sikka");
		ts.add("Chanda Kochhar");

		// according to natural ordering
		System.out.println("Sorted according"
				+ " to Natural-ordering:\n");
		for(String CEO : ts){
			System.out.println(CEO);
		}
	}
}

Output:

Sorted according to Natural-ordering:

Chanda Kochhar
Francisco D’Souza
Satya Nadella
Shantanu Narayen
Shiv Nadar
Sundar Pichai
Vishal Sikka

Note: All methods of TreeSet is non-synchronized

Q) How to make TreeSet synchronized ?

• TreeSet can be easily converted into synchronized TreeSet
• Using utility method synchronizedSet(ts); of java.util.Collections class

Set set = Collections.synchronizedSet(ts); 

Related Articles:

• Set interface
• HashSet class
• LinkedHashSet class
• SortedSet interface
• NavigableSet interface
• TreeSet class
• HashSet v/s LinkedHashSet
• HashSet v/s LinkedHashSet v/s TreeSet
• List v/s Set
• HashMap v/s HashSet

References:

• https://docs.oracle.com/javase/tutorial/collections/intro/
• https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html
• https://docs.oracle.com/javase/tutorial/collections/interfaces/list.html
• https://docs.oracle.com/javase/tutorial/collections/interfaces/set.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Set.html
• https://docs.oracle.com/javase/tutorial/collections/interfaces/sorted-set.html
• https://docs.oracle.com/javase/7/docs/api/java/util/SortedSet.html
• https://docs.oracle.com/javase/7/docs/api/java/util/NavigableSet.html
• https://docs.oracle.com/javase/7/docs/api/java/util/class-use/NavigableSet.html
• https://docs.oracle.com/javase/7/docs/api/java/util/TreeSet.html
• https://docs.oracle.com/cd/E21764_01/apirefs.1111/e17503/oracle/adfnmc/java/util/TreeSet.html
• https://docs.oracle.com/cd/E21764_01/apirefs.1111/e17503/index.html?oracle/adfnmc/java/util/TreeSet.html

Happy Coding !!
Happy Learning !!