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Java TreeMap firstKey() Method with Example

TreeMap Class firstKey() method: Here, we are going to learn about the firstKey() method of TreeMap Class with its syntax and example.
Submitted by Preeti Jain, on February 19, 2020

TreeMap Class firstKey() method

  • firstKey() method is available in java.util package.
  • firstKey() method is used to return the first key element with the least key value that exists in this TreeMap.
  • firstKey() 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.
  • firstKey() method may throw an exception at the time of returning the first key element with the lowest key value.
    NoSuchElementException: This exception may throw when this TreeMap is “blank”.


    public Key firstKey();


  • It does not accept any parameter.

Return value:

The return type of the method is Key, it retrieves first key element with the lowest key value.


// Java program to demonstrate the example 
// of Key firstKey() method of TreeMap 

import java.util.*;

public class FirstKeyOfTreeMap {
    public static void main(String[] args) {
        // Instantiates a TreeMap object
        TreeMap < Integer, String > tree_map = new TreeMap < Integer, String > ();

        // By using put() method is to add
        // key-value pairs in a TreeMap
        tree_map.put(20, "C");
        tree_map.put(50, "C++");
        tree_map.put(30, "JAVA");
        tree_map.put(10, "PHP");
        tree_map.put(60, "SFDC");

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

        // By using firstKey() method is to return
        // the first least key value
        // element exists in this TreeMap
        System.out.println("tree_map.firstKey(): " + tree_map.firstKey());


TreeMap: {10=PHP, 20=C, 30=JAVA, 50=C++, 60=SFDC}
tree_map.firstKey(): 10

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