TreeSet Class in Java with example

TreeSet Class in Java with example

Java TreeSet class which implements NavigableSet interface which is child interface of SortedSet interface. Objects in TreeSet class are stored in sorted ascending order.

TreeSet is similar to HashSet except that it sorts the elements in the ascending order while HashSet doesn’t maintain any insertion or ascending order.

TreeSet class Declaration

public class TreeSet extends AbstractSet

    implements NavigableSet, Cloneable, java.io.Serializable

{…}

Features of TreeSet class

1] Java TreeSet class is ultimately subclass of Set interface that’s why TreeSet class stores unique element only.

2] Java TreeSet class does not allow null , If we try to add null in TreeSet then at runtime it will throw java.lang.NullPointerException.

TreeSet set = new TreeSet<>();

set.add(123);

set.add(null);

Output

Exception in thread "main" java.lang.NullPointerException

      at java.util.TreeMap.put(TreeMap.java:563)

      at java.util.TreeSet.add(TreeSet.java:255)

      at com.vr.cls.TreeSetDemo.main(TreeSetDemo.java:10)

3] Java TreeSet class sorts the element in ascending order, So TreeSet does not preserve the insertion order of the element.

4] TreeSet does not allow inserting Heterogeneous objects. It will throw classCastException at Runtime if trying to add hetrogeneous objects.

public static void main(String[] args) {

           TreeSet set = new TreeSet<>();

           set.add(123);

           set.add("abc");

     System.out.println(set);

}

Output

Exception in thread "main" java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String

     at java.lang.String.compareTo(String.java:111)

     at java.util.TreeMap.put(TreeMap.java:568)

     at java.util.TreeSet.add(TreeSet.java:255)

5] Java TreeSet serves as an excellent choice for storing large amounts of sorted unique information which are supposed to be accessed quickly because of its access and retrieval times are quiet fast.

6] Java TreeSet class is not synchronized. If multiple threads access a tree set concurrently, and at least one of the threads modifies the set, it must be synchronized externally. 

SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));

7] The iterators returned by this class's iterator method are fail-fast:

Constructor and Description

TreeSet set = new TreeSet()

Constructs a new, empty tree set, sorted according to the natural ordering of its elements.

TreeSet set = new TreeSet(Collection c)

Constructs a new tree set containing the elements in the specified collection, sorted according to the natural ordering of its elements.

TreeSet set = new TreeSet(Comparator comparator)

Constructs a new, empty tree set, sorted according to the specified comparator.

TreeSet set = new TreeSet(SortedSet s)

Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set.

Java TreeSet Example

package com.vr.techfloaters;

import java.util.TreeSet;

public class TreeSetDemo {

    

     public static void main(String[] args) {

           TreeSet set = new TreeSet<>();

          

           //Similier datatype elements are added using add() method

           set.add(123);

           set.add(879);

           set.add(456);

          

           //Duplicate not be inserted

           set.add(123);

          

           //Can not insert null at Runtime throws java.lang.NullPointerException

           //set.add(null);

          

           //Different data type can not insert at runtime it throws java.lang.NullPointerException

           //set.add("abc");

          

           //print in ascending order

           System.out.println(set);

     }

}

Output

[123, 456, 879]