How to Extend HashMap to Allow String, String Types in Java

How can I extend HashMap to only allow String keys and String values in Java?

class StringStringHashMap extends HashMap<String, String> {
    @Override
    public String put(String key, String value) {
        if (key == null || value == null) {
            throw new IllegalArgumentException("Keys and values cannot be null");
        }
        return super.put(key, value);
    }
}

In Java, HashMap is a part of the Java Collection Framework that enables the storage of key-value pairs. To create a specialized version of HashMap that restricts the types of keys and values to Strings, you can extend the HashMap class and implement custom behavior as needed.

class StringStringHashMap extends HashMap<String, String> {
    @Override
    public String put(String key, String value) {
        if (key == null || value == null) {
            throw new IllegalArgumentException("Keys and values cannot be null");
        }
        return super.put(key, value);
    }
}

Causes

• HashMap allows any Object type as key and value, leading to potential type safety issues.
• Custom implementation might be needed to enforce specific rules, like null checking or type consistency.

Solutions

• Extend the HashMap class and specify types as Map<String, String>.
• Override methods like put() to enforce type and null checks.

Mistake: Not checking for null keys and values before adding to the HashMap.

Solution: Implement a check in the overridden put() method to throw an exception if nulls are encountered.

Mistake: Forgetting that the base HashMap allows any object type, leading to type safety issues.

Solution: Use generics appropriately, which helps in restricting types and improving code clarity.