TreeMap firstEntry() Method in Java with Examples

TreeMap firstEntry() refers to the method used to retrieve the key-value pairs mapped with the lowest key value element that exists in the TreeMap, if there are no key-value pairs within the Map, simply returns null. The method name ‘firstEntry()’ explains itself that it will return entry having the least key element with its value.

Syntax: public Map.Entry<K,V> firstEntry(), 

Here K and V refer key-value respectively.

Parameters: NA - As it doesnot accept any parameter.

Return Value: It returns an entry with the least key (lowest key-value pair) and null if the 
TreeMap is empty.

Exception: NA - As it doesnot throw any exception at entry return.

Example 1:

Java

// Java code to demonstrate
// the working of TreeMap firstKey()
import java.io.*;
import java.util.*;
public class treeMapFirstKey {
public static void main(String[] args)
    {

        // Declaring the TreeMap of Key - Value Pairs
        // Integer - Key , String - Value
        TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();

        // Adding-up the values in the TreeMap
        // Use put() function to append data
        treemap.put(2, "Java");
        treemap.put(4, "CPP");
        treemap.put(5, "PHP");
        treemap.put(1, "Python");
        treemap.put(3, "C");

        // Check for firstEntry()
        System.out.println("Lowest Entry is: " + treemap.firstEntry());
    }
}

Output

Lowest Entry is: 1=Python

By the above example, it’s clear that firstEntry() checks compare each key of TreeMap, and returns having the least key-value pair.

Example 2:

Java

// Java code to demonstrate the working
// of TreeMap firstKey() method
import java.io.*;
import java.util.*;
public class percentageFirstKey {
public static void main(String[] args)
    {

        // Declaring the TreeMap of Key - Value Pairs
        // Double - Key , String - Value
        TreeMap<Double, String> treemapPercentage = new TreeMap<Double, String>();

        // Adding-up the values in the TreeMap
        // Use put() function to append data
        treemapPercentage.put(81.40, "Shashank");
        treemapPercentage.put(72.80, "Anand");
        treemapPercentage.put(65.50, "Gulshan");
        treemapPercentage.put(71.10, "Abhishek");
        treemapPercentage.put(70.20, "Ram");

        // Check for firstEntry()
        System.out.println("Lowest Entry is: " + treemapPercentage.firstEntry());
    }
}

Output

Lowest Entry is: 65.5=Gulshan

Some points on TreeMap firstEntry():

• TreeMap firstEntry() is available in java.util package.
• It does not throw an exception at return entry time.
• TreeMap firstEntry() method is a non-static method as it is accessible by the class’s object, other than that, will get an error.