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# What is the TreeSet.add() function in Java?

Vinisha Maheshwari

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The TreeSet.add() method of the TreeSet class in Java adds a particular element into a TreeSet object. TreeSet.add() only adds that particular element if the TreeSet object does not already contain it.

To use the TreeSet.add() method, you need to import the java.util package, as shown below.

import java.util.TreeSet


### Parameters

• element: The element to be added to the TreeSet object. The data type of this parameter should be the same as the data type of the TreeSet instance.

### Return value

If element is not present in the TreeSet object, the TreeSet.add() method adds it to the TreeSet and returns true. Otherwise, TreeSet.add() does not add the element and returns false.

### Example

Consider the following list of elements to be added to a TreeSet object:

• [$1, 8, 5, 8, 3$]

The TreeSet.add() method would result in the TreeSet below:

• [$1, 8, 5, 3$]

• The first element is $1$, which was not already in the TreeSet, so $1$ is added to the TreeSet.

• Similarly, the second element is $8$, which was not already in the TreeSet, so $8$ is added to the TreeSet.

• The third element is $5$, which was not already in the TreeSet, so $5$ is added to the TreeSet.

• The fourth element is $8$, which was already present in the TreeSet, so $8$ is not added to the TreeSet.

• The final element is $3$, which was not already in the TreeSet, so $3$ is added to the TreeSet.

The TreeSet stores [1,3,5,8] in the sorted order.

### Code

The code below shows how the TreeSet.add() method works in Java.

import java.io.*;import java.util.TreeSet;class Main {    public static void main(String args[])    {        TreeSet<Integer> tree_set = new TreeSet<Integer>();        tree_set.add(1);        tree_set.add(8);        tree_set.add(5);        tree_set.add(8);        tree_set.add(3);        tree_set.add(0);        System.out.println("TreeSet: " + tree_set);    }}

### Explanation

In the code above:

• Lines 1 and 2 import the required packages and classes.

• In line 4, we initiate the Main class.

• In line 8, we initialize a TreeSet object of type int.

• In lines 9 to 14, we add elements to the TreeSet object through the TreeSet.add() method.

• In line 15, we display the final TreeSet.

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