TreeSet

TreeSet Constructors

There are four Constructors in a TreeSet: 

• TreeSet ts = new TreeSet(); //This method creates an empty TreeSet object in which elements are inserted in the natural sorting order.

Here is an example of TreeSet:

import java.util.*;
public class Main {
    public static void main(String[] args) {
        TreeSet ts = new TreeSet();

        //adding elements in the TreeSet using add()
        ts.add("1");
        ts.add("4");
        ts.add("2");
        ts.add("0");

        //printing the TreeSet
        System.out.println("TreeSet is: " + ts);
    }
}

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Output:

TreeSet is: [0, 1, 2, 4]

• TreeSet ts = new TreeSet(Comparator c); //This constructor creates an empty TreeSet object with customized sorting described by the comparator operator.
   
• TreeSet ts = new TreeSet(Collection c); //This constructor creates a TreeSet object which consists of all the elements from the collection and stores them in the natural sorting order by default.
   
• TreeSet ts = new TreeSet(SortedSet s); //The constructor builds a TreeSet object that holds all elements in the given sorted set in the order they were parsed.

Here is an implementation for the same:

import java.util.*;
public class Main {
    public static void main(String[] args) {
        // Creating TreeSet object
        TreeSet < Integer > ts = new TreeSet < Integer > ();

        // Adding elements in the TreeSet using add()
        ts.add(5);
        ts.add(1);
        ts.add(7);
        ts.add(3);
        ts.add(6);
        ts.add(0);

        // Printing the elements
        System.out.println("TreeSet: " + ts);

        //here we are returning a subset between 4 and 9 to a sortedSet data
        SortedSet < Integer > ss = ts.subSet(4, 9);

        //With the help of sortedSet data we are creating a treeSet
        TreeSet < Integer > ts_1 = new TreeSet < Integer > (ss);

        //printing the new treeset
        System.out.println(ts_1);
    }
}

You can also try this code with Online Java Compiler

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Output:

TreeSet: [0, 1, 3, 5, 6, 7]
[5, 6, 7]

Try it by yourself on java online compiler.

Some points to remember:

• Objects should be homogeneous and comparable if we rely on the default natural sorting order. Otherwise, we will get a class casting exception runtime error.
• Comparable objects are those whose corresponding classes implement the Java.lang.comparable interface.
• This interface is already implemented by the String Class and all wrapper classes. In contrast, StringBuffer does not implement anything similar. As a result, we get a ClassCastException.

TreeSet Methods

Frequently Asked Questions

When will a TreeSet throw a NullPointerException?

Null insertion is possible for empty TreeSets as the first element. However, if we attempt to insert another element after inserting null, we will receive a NullPointerException.

Is the TreeSet synchronized?

A TreeSet cannot be synchronized because a TreeSet can be modified by multiple threads simultaneously, and each thread must update the set within a synchronized manner.
TreeSet ts = Collections.syncronizedSortedSet(new TreeSet());

What is the time complexity of a TreeSet?

A TreeSet's add(), remove(), and contains() methods are guaranteed to be Big O (log n) complex.

What is the difference between HashSet and TreeSet.

 You can also read about the topic -  hash function in data structure

Conclusion

In this blog, we have seen what is TreeSet in the Collection Framework and also the methods of TreeSet.

Check out this problem - Duplicate Subtree In Binary Tree

We hope that this blog has helped you enhance your knowledge about TreeSet and if you would like to learn more, check out our articles on the link. Do upvote our blog to help other ninjas grow. Happy Coding!