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Java AbstractMap hashCode() Method - GeeksforGeeks

Last Updated : 11 Jul, 2025

The hashCode() method of the AbstractMap class in Java is used to calculate a hash code value for a map. This hash code is based on the key-value mapping contained in the map. It ensures consistency such that two maps with the same entries have the same hash code.

Example 1: Hash Code of a Non-Empty Map

// Java program demonstrate the working of hashCode()
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.Map;

public class Geeks {
    public static void main(String[] args)
    {
        // Create a HashMap
        Map<String, Integer> hm = new HashMap<>();

        // Add key-value pairs
        hm.put("Java", 1);
        hm.put("Programnming", 2);
        hm.put("Language", 3);

        // Get hashCode
        System.out.println("Map: " + hm);
        System.out.println("HashCode: " + hm.hashCode());
    }
}

Map: {Programnming=2, Java=1, Language=3}
HashCode: -95421541

Explanation: In the above example, it creates a HashMap and adds three key-value pairs to it. The hashCode() method calculates a unique integer value based on the keys and values in the map.

public int hashCode()

Return Type: It returns an integer representing the hash code value of the map.

Example 2: Hash Code of an Empty Map

// Java programm to demonstrates the 
// hash code of an empty HashMap
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.Map;

public class Geeks {
    public static void main(String[] args)
    {

        // creating an empty HashMap
        Map<String, Integer> hm1 = new HashMap<>();
        System.out.println("Empty Map: " + hm1);
        System.out.println("HashCode of Empty Map: "
                           + hm1.hashCode());
    }
}

Empty Map: {}
HashCode of Empty Map: 0

Explanation: The above program creates an empty HashMap without any key-value pairs. The hashCode() method returns 0 because no entries exist in the map.

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