Скачать или смотреть How to Make a Private HashMap Visible to Other Classes in Java

Learn how to share a private `HashMap` across classes in Java using getters without compromising encapsulation.
---
This video is based on the question https://stackoverflow.com/q/70405704/ asked by the user 'Slaven Stajić' ( https://stackoverflow.com/u/15157202/ ) and on the answer https://stackoverflow.com/a/70406799/ provided by the user 'WJS' ( https://stackoverflow.com/u/1552534/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to make private hashmap in one class visible to other class

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Make a Private HashMap Visible to Other Classes in Java

In programming, particularly in object-oriented languages like Java, one commonly emphasized principle is encapsulation. This means that class properties should be kept private to avoid unintended interaction and potential bugs in larger programs. However, what if you need to access these private properties from another class? In this guide, we will tackle a common scenario you might face: how to make a private HashMap in one class visible to another class.

Understanding the Problem

While designing a program, you may encounter a situation where you want to keep class fields private for better encapsulation. For example, in the context of an air traffic management system, you may have a HashMap in an Airplane class to keep track of airplanes and their capacities. However, trying to access this HashMap directly from another class, such as an interface class, results in visibility errors due to its private access modifier.

Here's the basic idea of your current implementation:

You've created a HashMap in the Airplane class.

You've made this HashMap private, which is good for encapsulation.

You want to access this HashMap in another class but are facing visibility issues.

Solution: Using Getters to Access Private Fields

The solution to your problem is straightforward: use getter methods. A getter method allows you to retrieve the private HashMap without exposing the ability to modify it directly. Here's how you can accomplish this:

Step-by-Step Implementation

Declare the HashMap:
Keep your HashMap private as before to maintain encapsulation.

[[See Video to Reveal this Text or Code Snippet]]

Create a Getter Method:
Add a getter method in your Airplane class that returns the HashMap. You might want to return an unmodifiable version of the HashMap to prevent external modifications.

[[See Video to Reveal this Text or Code Snippet]]

Access the HashMap from Other Classes:
In your other classes (e.g., the interface class), you can now access this HashMap through the getter method, preventing direct manipulation:

[[See Video to Reveal this Text or Code Snippet]]

Benefits of Using Getters

Encapsulation: The internal representation of your class remains hidden, allowing for flexibility if you decide to change its implementation in the future.

Controlled Access: Users of your class can retrieve values without altering them, which is particularly important for collections like HashMap.

Defensive Programming: Using unmodifiableMap ensures that no changes are made to the underlying collection by other parts of the program.

By following these steps, you will keep your code organized without compromising the principles of encapsulation and data hiding.

Conclusion

In conclusion, when you're faced with the need to share a private HashMap between classes in Java, utilizing getter methods is an effective approach. By allowing controlled access to your private fields, you maintain the integrity of your objects while still providing the functionality needed for your application.

Happy coding! If you have further questions or need additional clarification, feel free to reach out in the comments below.