TreeMap firstEntry() and firstKey() Method in Java with Examples
There are two variants of first() in Java.util.TreeMap, both are discussed in this article.
Method 1: firstEntry()
It returns a key-value mapping associated with the least key in this map, or null if the map is empty.
Syntax:
public Map.Entry firstEntry()
Return Type: An entry with the least key and null if the map is empty.
Example:
Java
Output:
Lowest entry is: 1=one
Method 2: firstKey()
It returns the first (lowest) key currently in the map.
Syntax:
public K firstKey()
Return Type: The first (lowest) key currently in this map.
Exception Thrown: NoSuchElementException is thrown if this map is empty.
Example:
Java
// Java Program to Demonstrate firstKey() Method // of TreeMap class // Importing required classes import java.io.*; import java.util.*; // Main class class GFG { // Main driver method public static void main(String[] args) { // Creating an empty TreeMap by // declaring object of integer, strings pairs TreeMap<Integer, String> treemap = new TreeMap<Integer, String>(); // Populating values in the TreeMap // using put() method treemap.put( 2 , "two" ); treemap.put( 1 , "one" ); treemap.put( 3 , "three" ); treemap.put( 6 , "six" ); treemap.put( 5 , "five" ); treemap.put( 9 , "nine" ); // Printing the lowest entry in TreeMap by // using firstKey() method System.out.println( "Lowest key is: " + treemap.firstKey()); } } |
Output:
Lowest key is: 1
Implementation: These functions can be used to fetch the best-ranked person in the given list, or can be used to assign a winner in which person with the lowest time to finish a task wins. The latter one is discussed below.
Example: Practical Application
Java
// Java Program to Demonstrate Application Usage // of firstKey() and firstEntry() Methods // of TreeMap class // Importing required classes import java.io.*; import java.util.*; // Main class public class GFG { // Main driver method public static void main(String[] args) { // Creating an empty TreeMap // of Integer and String times of participants // In seconds TreeMap<Float, String> time = new TreeMap<Float, String>(); // Populating the time taken to complete task // using put() method time.put( 2 .32f, "Astha" ); time.put( 7 .43f, "Manjeet" ); time.put( 1 .3f, "Shambhavi" ); time.put( 5 .63f, "Nikhil" ); time.put( 6 .26f, "Vaishnavi" ); // Printing person with least time // using of firstEntry() method System.out.println( "Winner with lowest time is : " + time.firstEntry()); } } |
Output:
Winner with lowest time is : 1.3=Shambhavi