Checking if two HashMaps are equal in Java

23 Oct 2023

In Java, HashMap is a widely-used class in the java.util package, which allows us to store key-value pairs. Often, we may need to compare two HashMap objects to see if they are equal. In this blog post, we will explore different ways to accomplish this task.

Approach 1: Comparing Key-Value Pairs

One way to check if two HashMap objects are equal is by comparing their key-value pairs. We can iterate over the entries of each HashMap and compare the keys and values one by one.

Here is an example code snippet:

import java.util.HashMap;
import java.util.Map;

public class HashMapComparisonExample {
    public static void main(String[] args) {
        Map<Integer, String> map1 = new HashMap<>();
        map1.put(1, "value1");
        map1.put(2, "value2");

        Map<Integer, String> map2 = new HashMap<>();
        map2.put(1, "value1");
        map2.put(2, "value2");

        boolean isEqual = true;

        if (map1.size() != map2.size()) {
            isEqual = false;
        } else {
            for (Map.Entry<Integer, String> entry : map1.entrySet()) {
                Integer key = entry.getKey();
                String value = entry.getValue();
                if (!map2.containsKey(key) || !map2.get(key).equals(value)) {
                    isEqual = false;
                    break;
                }
            }
        }

        System.out.println("Are the HashMaps equal? " + isEqual);
    }
}

In this example, we create two HashMap objects, map1 and map2, with the same key-value pairs. We iterate over the entries of map1, check if the corresponding key exists in map2, and compare the values. If any key-value pair doesn’t match or if the sizes of the two maps are different, we set isEqual to false.

Approach 2: Using `Equals` Method

Another way to compare two HashMap objects for equality is to use the equals method provided by the HashMap class. This method compares the key-value pairs of two maps and returns true if they are equal.

Here is an example code snippet showcasing this approach:

import java.util.HashMap;
import java.util.Map;

public class HashMapComparisonExample {
    public static void main(String[] args) {
        Map<Integer, String> map1 = new HashMap<>();
        map1.put(1, "value1");
        map1.put(2, "value2");

        Map<Integer, String> map2 = new HashMap<>();
        map2.put(1, "value1");
        map2.put(2, "value2");

        boolean isEqual = map1.equals(map2);

        System.out.println("Are the HashMaps equal? " + isEqual);
    }
}

In this example, we use the equals method to compare map1 and map2. The method internally compares the key-value pairs of both maps, returning true if they are equal.

Conclusion

In this blog post, we explored two different approaches to check if two HashMap objects are equal in Java. The first approach involved comparing key-value pairs, while the second approach used the equals method provided by the HashMap class. Depending on the context and requirements of your application, you can choose the most appropriate approach.

Remember to consider the complexity of your implementation and the runtime performance when comparing large HashMap objects.

#References

#Java #HashMaps

Approach 1: Comparing Key-Value Pairs

Approach 2: Using Equals Method

Conclusion

Approach 2: Using `Equals` Method