TreeSet in Java

What is TreeSet?

• Stores unique elements.
• Maintains elements in sorted order (ascending by default).
• Does not allow duplicates.
• It is part of the Java Collections Framework in Java and implements the Set interface.

Example :

import java.util.TreeSet;

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

        TreeSet tr = new TreeSet();
        tr.add(1000);
        tr.add(300);
        tr.add(500);
        tr.add(10);
        System.out.println(tr);

    }
}

//Even though we inserted 1000 first, TreeSet keeps them sorted.

Output: [10, 300, 500, 1000]

Duplicate Example :

import java.util.TreeSet;

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

        TreeSet tr = new TreeSet();
        tr.add(1000);
        tr.add(1000);
        tr.add(500);
        tr.add(500);
        System.out.println(tr);

    }
}

//Duplicate values are ignored.

Output : [500, 1000]

Null Example :

import java.util.TreeSet;

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

        TreeSet tr = new TreeSet();
        tr.add(null);
        System.out.println(tr);

    }
}

//TreeSet does not allow null.

Output : NullPointerException

Important TreeSet Methods:

add():

• To add element/Object.

tr.add(500);

remove():

• To remove element/Object.

tr.remove(500);

contains():

• To check if element/Object exist.

tr.contains(500);

size():

• To find the number of elements/objects.

tr.size();

first():

• To find the smallest element/object.

tr.first();

last():

• To find the largets element/object.

tr.last();

higher():

• To find the next greater element/object.

tr.higher(50);

lower():

• To find the previous element/object.

tr.lower(200);

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

        TreeSet tr = new TreeSet();
        tr.add(500);
        tr.add(200);
        tr.add(1000);
        tr.add(50);
        tr.add(10);
        System.out.println(tr);
        tr.remove(500);
        System.out.println(tr);
        System.out.println(tr.size());
        System.out.println(tr.first());
        System.out.println(tr.last());
        System.out.println(tr.higher(50));
        System.out.println(tr.lower(200));



    }
}

Output: 

[10, 50, 200, 500, 1000] //add
[10, 50, 200, 1000]      //remove element 500
4                        //size
10                       //first element
1000                     //last element
200                      //next higher to element 50
50                       //next lower to element 200