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HashMap size() Method in Java

  • Difficulty Level : Basic
  • Last Updated : 26 Nov, 2018

The java.util.HashMap.size() method of HashMap class is used to get the size of the map which refers to the number of the key-value pair or mappings in the Map.

Syntax:

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Hash_Map.size()

Parameters: The method does not take any parameters.

Return Value: The method returns the size of the map which also means the number of key-value pairs present in the map.



Below programs illustrates the working of java.util.HashMap.size():
Program 1: Mapping String Values to Integer Keys.




// Java code to illustrate the size() method
import java.util.*;
  
public class Hash_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty HashMap
        HashMap<Integer, String> hash_map = new HashMap<Integer, String>();
  
        // Mapping string values to int keys
        hash_map.put(10, "Geeks");
        hash_map.put(15, "4");
        hash_map.put(20, "Geeks");
        hash_map.put(25, "Welcomes");
        hash_map.put(30, "You");
  
        // Displaying the HashMap
        System.out.println("Initial Mappings are: " + hash_map);
  
        // Displaying the size of the map
        System.out.println("The size of the map is " + hash_map.size());
    }
}
Output:
Initial Mappings are: {20=Geeks, 25=Welcomes, 10=Geeks, 30=You, 15=4}
The size of the map is 5

Program 2: Mapping Integer Values to String Keys.




// Java code to illustrate the size() method
import java.util.*;
  
public class Hash_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty HashMap
        HashMap<String, Integer> hash_map = new HashMap<String, Integer>();
  
        // Mapping int values to string keys
        hash_map.put("Geeks", 10);
        hash_map.put("4", 15);
        hash_map.put("Geeks", 20);
        hash_map.put("Welcomes", 25);
        hash_map.put("You", 30);
  
        // Displaying the HashMap
        System.out.println("Initial Mappings are: " + hash_map);
  
        // Displaying the size of the map
        System.out.println("The size of the map is " + hash_map.size());
    }
}
Output:
Initial Mappings are: {4=15, Geeks=20, You=30, Welcomes=25}
The size of the map is 4

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




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