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The pollFirst() method of TreeSet in Java is used to retrieves and removes the first (lowest) element, or returns null if this TreeSet is empty. Syntax:

E pollFirst()

Where, E is the type of elements maintained by this TreeSet container. Parameters: This function does not accepts any parameter. Return Type:It returns the first element of the Treeset if TreeSet is not empty else returns null. Below programs illustrate the pollFirst() method in Java: Example 1

Java

// A Java program to demonstrate
// pollFirst() method of TreeSet

import java.util.TreeSet;

public class GFG {
    public static void main(String[] args)
    {
        // creating TreeSet
        TreeSet<Integer> ts = new TreeSet<Integer>();

        // adding element to the TreeSet
        ts.add(0);
        ts.add(1);
        ts.add(2);
        ts.add(3);
        ts.add(4);
        ts.add(5);
        ts.add(6);

        // before removing element
        System.out.println("Before removing " + 
                   "element from TreeSet: " + ts);

        // first element is removed
        System.out.println("First lowest element " + 
                 "removed is : " + ts.pollFirst());
        System.out.println("After removing element" + 
                             " from TreeSet: " + ts);
    }
}

Output:

Before removing element from TreeSet: [0, 1, 2, 3, 4, 5, 6]
First lowest element removed is : 0
After removing element from TreeSet: [1, 2, 3, 4, 5, 6]

Example 2

Java

// A Java program to demonstrate
// pollFirst() method of TreeSet

import java.util.TreeSet;

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

        // removing element when TreeSet
        // is empty
        System.out.println("pollFirst() method when " + 
             "TreeSet is empty  :  " + ts.pollFirst());

        // adding element to the TreeSet
        ts.add("Geeks");
        ts.add("for");
        ts.add("Geek");

        // before removing element
        System.out.println("Before removing element from" + 
                                      " TreeSet: " + ts);

        // first element is removed
        System.out.println("First lowest element removed is : "
                           + ts.pollFirst());
        System.out.println("After removing element " + 
                               "from TreeSet: " + ts);
    }
}

Output:

pollFirst() method when TreeSet is empty  :  null
Before removing element from TreeSet: [Geek, Geeks, for]
First lowest element removed is : Geek
After removing element from TreeSet: [Geeks, for]

If TreeSet is empty, then this method returns null. Example 3

Java

// A Java program to demonstrate
// pollFirst() method of TreeSet

import java.util.TreeSet;

public class GFG {
    public static void main(String[] args)
    {
        // creating TreeSet
        TreeSet<Integer> ts = new TreeSet<Integer>();

        // before removing element
        System.out.println("Before removing " + 
                   "element from TreeSet: " + ts);

        // first element is removed
        System.out.println("First lowest element " + 
                 "removed is : " + ts.pollFirst());
        System.out.println("After removing element" + 
                             " from TreeSet: " + ts);
    }
}

Output:

Before removing element from TreeSet: []
First lowest element removed is : null
After removing element from TreeSet: []

TreeSet pollFirst() method in Java

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