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Java TreeMap pollFirstEntry() Method with Example

TreeMap Class pollFirstEntry() method: Here, we are going to learn about the pollFirstEntry() method of TreeMap Class with its syntax and example.
Submitted by Preeti Jain, on February 29, 2020

TreeMap Class pollFirstEntry() method

• pollFirstEntry() method is available in java.util package.
• pollFirstEntry() method is used to return and then remove the entry (key-value pair) linked with the lowest key element value that exists in this TreeMap.
• pollFirstEntry() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.
• pollFirstEntry() method does not throw an exception at the time of returning first entry.

Syntax:

    public Map.Entry pollFirstEntry();

Parameter(s):

• It does not accept any parameter.

Return value:

The return type of the method is Map.Entry, it retrieves an entry with the lowest key element value when exists otherwise it returns null.

Example:

// Java program to demonstrate the example 
// of Map.Entry pollFirstEntry () 
// method of TreeMap 

import java.util.*;

public class PollFirstEntryOfTreeMap {
    public static void main(String[] args) {
        // Instantiates TreeMap
        TreeMap < Integer, String > tm = new TreeMap < Integer, String > ();

        // By using put() method is
        // to put the key-value pairs in
        // treemap tm
        tm.put(1, "C");
        tm.put(4, "C++");
        tm.put(3, "Java");
        tm.put(2, "Php");

        // Display TreeMap tm
        System.out.println("tm: " + tm);

        // By using pollFirstEntry() method is to
        // return and remove the key-value pairs
        // linked with the least key element value
        // i.e. "1"
        tm.pollFirstEntry();

        // Display updated TreeMap tm
        System.out.println("tm.pollFirstEntry(): " + tm);
    }
}

Output

tm: {1=C, 2=Php, 3=Java, 4=C++}
tm.pollFirstEntry(): {2=Php, 3=Java, 4=C++}