Efficiently Check Models in LinkedHashMap using Generics in Java

Discover how to create a generic method in Java that checks for a model's existence in `LinkedHashMap` without redundancy. Learn to streamline your code with examples!
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This video is based on the question https://stackoverflow.com/q/70074162/ asked by the user 'phamous' ( https://stackoverflow.com/u/4231356/ ) and on the answer https://stackoverflow.com/a/70074224/ provided by the user 'magicmn' ( https://stackoverflow.com/u/9712270/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Efficiently Check Models in LinkedHashMap using Generics in Java

When working with collections in Java, specifically LinkedHashMap, you may find yourself in a situation where you need to manage multiple subclasses of a common superclass. In this case, let's dive into how to create a reusable, generic method that can check the presence of a model across various LinkedHashMap instances without duplicating code.

The Problem

Imagine you have a superclass called Car with several subclasses, like Honda, Toyota, and Lexus. You’ve created three separate LinkedHashMaps tailored to each subclass:

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As you can see, this leads to repetitive code if you need to check for the existence of a vehicle model in each of these maps. Thus, the need arises: Can you create a generic method that accomplishes this?

The Solution: Using Generics

The answer is yes! You can achieve this by implementing a generic method that allows you to check if a LinkedHashMap contains a specific model based on the string key. Here's how you can do it.

Using Wildcards to Simplify

Basic Usage: If your core requirement is to simply check if the map contains the key, the ? wildcard will suffice. Here’s a method that accomplishes just that:

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This method accepts any map as long as the key is a String. The wildcard ? allows flexibility in the types of values stored.

Restricting to Specific Types (Optional)

Refining the Method: If you want your method to only accept maps that contain a String key and values that extend the Car class, you can specify that in your method signature:

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This means your method is now limited to check LinkedHashMap instances where the value must be an object of type Car or any subtype of Car.

Benefits of This Approach

Code Reusability: You eliminate the need for three separate methods for each type of car. This makes maintaining the codebase much easier as you have a single point of change.

Clarity: The method signatures clearly convey the intent and constraints regarding the types of maps you're handling.

Flexibility: You can easily extend this method later if you want to include more car types without changing the core logic.

Conclusion

By utilizing generics and wildcards in Java, you can efficiently manage and query collections of different subclasses without redundancy in your code. This not only streamlines your logic but also adheres to the principles of code reusability and clarity. The next time you find yourself with similar situations, apply this method to create elegant solutions in your Java applications!