Last Updated : 20 Nov, 2021
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
// Java Program to Illustrate Working of firstKey() Method
// 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 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(7, "seven");
treemap.put(3, "three");
treemap.put(1, "one");
treemap.put(6, "six");
treemap.put(9, "nine");
// Printing the lowest entry in TreeMap by
// using firstEntry() method
System.out.println("Lowest entry is: "
+ treemap.firstEntry());
}
}
Output:
Lowest entry is: 1=oneMethod 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
RetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4