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TreeMap keySet() Method in Java with Examples

  • Last Updated : 10 Dec, 2021

In Java, keySet() method of TreeMap class is present inside java.util package in Java is used to create a set out of the key elements contained in the treemap. It basically returns a set view of the keys or we can create a new set and store the key elements in them in ascending order. Since the set is backed by the map, any changes made to the map are reflected in the set, and vice-versa.

--> java.util Package
    --> TreeMap Class
        --> keySet() Method  

Syntax: 

tree_map.keySet()

Return Type: A set having the keys of the treemap in ascending order.

Example 1: Mapping String Values to Integer Keys. 

Java




// Java Program to illustrate the keySet() method
// of TreeMap class where we are
// Mapping String Values to Integer Keys
 
// Importing required classes
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, string pairs
        TreeMap<Integer, String> tree_map
            = new TreeMap<Integer, String>();
 
        // Mapping string values to int keys
        // using put() method
        tree_map.put(10, "Geeks");
        tree_map.put(15, "4");
        tree_map.put(20, "Geeks");
        tree_map.put(25, "Welcomes");
        tree_map.put(30, "You");
 
        // Printing the elements of above TreeMap
        System.out.println("Initial Mappings are: "
                           + tree_map);
 
        // Getting the set view of keys
        // using keySet() method
        System.out.println("The set is: "
                           + tree_map.keySet());
    }
}
Output: 
Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
The set is: [10, 15, 20, 25, 30]

 

Example 2: Mapping Integer Values to String Keys

Java




// Java Program to Illustrate keySet() Method
// of TreeMap class where we are
// Mapping Integer Values to String Keys
 
// Importing required classes
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 string, integer pairs
        TreeMap<String, Integer> tree_map
            = new TreeMap<String, Integer>();
 
        // Mapping int values to string keys
        // using put() method
        tree_map.put("Geeks", 10);
        tree_map.put("4", 15);
        tree_map.put("Geeks", 20);
        tree_map.put("Welcomes", 25);
        tree_map.put("You", 30);
 
        // Printing the elements of TreeMap
        System.out.println("Initial Mappings are: "
                           + tree_map);
 
        // Getting the set view of keys
        // using keySet() method
        System.out.println("The set is: "
                           + tree_map.keySet());
    }
}
Output: 
Initial Mappings are: {4=15, Geeks=20, Welcomes=25, You=30}
The set is: [4, Geeks, Welcomes, You]

 

Note: Similarly the same operation can be performed with any type of Mappings with variation and combination of different data types.


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