How Can You Implement a Map with Multiple Keys in Java?

Implementing a Map with Multiple Keys

A common need in programming is a data structure that acts like a map, but with the ability to access values using multiple (differently-typed) keys. While a typical map associates a key of a single type with a corresponding value, this requirement demands a more flexible approach.

Solution: Two Maps Instead of One

Due to the nature of maps, using a composite key (e.g., a tuple or pair) to represent the multiple keys in Java would not suffice. This is because maps rely on hash codes and equality checks for key lookups. Hence, it becomes impossible to search for values using only one of the components of the composite key.

Instead, the recommended solution is to maintain two separate maps internally: one Map and one Map. This allows for efficient access to values using either key type.

Implementation with a Wrapper Class

If a single interface is desired, a wrapper class can be created to expose the methods for accessing values by either key. This wrapper class would delegate the actual lookups to the two underlying maps, providing a unified interface for the user.

Conclusion

By using two maps internally and potentially implementing a wrapper class, it is possible to implement a data structure that behaves like a map with multiple keys. This approach ensures efficient retrieval of values using either key type while maintaining the uniqueness of the keys.

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