To evaluate a class that includes private methods, fields, or inner classes, various techniques such as reflection, utility classes, and test doubles can be employed to assess their functionality.
In this article, we will explore in-depth how to evaluate a class that features private methods, fields, or inner classes.
What are Private Methods, Fields, and Inner Classes in Java
Private Methods: Private methods are those that can only be accessed within the class they are defined in. They facilitate the encapsulation of the class’s functionality and can decompose complex logic into simpler parts.
Private Fields: Private fields are variables exclusively accessible within the class where they are declared. They maintain the internal state and data that should not be manipulated externally, aiding encapsulation and preventing direct access from other classes.
Inner Classes: Inner classes are defined within another class. They serve to encapsulate a single class and have the ability to access the private members of the outer class.
Techniques to Evaluate Classes with Private Methods, Fields, or Inner Classes
Assessing a class that comprises private methods, fields, or inner classes can be challenging, but several techniques are available. Some include:
Utilize Public Methods
Implement Reflection
Apply Inner Classes for Evaluating Private Inner Classes
Implement Package-Private Access
Utilize PowerMock
Method 1: Utilize Public Methods (General Approach, Best Practice)
This is the simplest and most effective method for evaluating private methods. In this approach, evaluation is performed indirectly via public methods. Since private methods are typically invoked within public methods, testing them through public access automatically verifies the functionality of the private methods.
Example:
done by indirectly testing through the public methods. Since private methods are usually used inside public methods, testing them publicly will automatically check if the private methods are working correctly or not.
Example:
Java
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Clarification:
In the aforementioned Java code, the Calculator class contains a private method, add(int a, int b), which cannot be employed directly from outside the class. Consequently, the public method addNumbers(int x, int y) invokes the private method and returns the outcome.
Approach 2: Utilizing Reflection in Java
Reflection is a capability in Java that permits you to examine a class and access its private components, even if they are concealed. It facilitates the reading and modification of private fields, invocation of private methods, and access to private inner classes.
Illustration:
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Outcome:
Clarification:
The preceding Java code employs Reflection to access and invoke a private method called add() from the Calculator class. It subsequently utilizes the setAccessible method to permit accessibility to the private method, and then calls it with the arguments 5 and 10.
Approach 3: Implementing Inner Classes for Testing Private Inner Classes
If a class contains a class designated as private, it cannot be utilized from outside...
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externally. Thus, to evaluate a private inner class, you may establish a testing class in the identical directory to utilize it in an indirect manner.
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Outcome:
Clarification:
In the aforementioned Java code, the OuterClass encompasses a private inner class with a private method getSecretMessage(). Given that both the inner class and its methods are private, they cannot be accessed by external classes.
Method 4: Utilize Package-Private Access
This approach permits the classes to be employed solely by those present in the same packages, including testing classes as well. It serves as a straightforward method to facilitate testing.
Illustration:
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Output:
Clarification:
In the Java code above, the add() function is not designated as private, so it can be directly accessed by other classes within the same package, such as the Main class. This will enable you to easily test or utilize it without having to declare it as public or resorting to reflections.
Method 5: Employ PowerMock
When there's a necessity to access private methods in Java, PowerMock (used alongside Mockito) stands as one of the most robust options. Since private methods are not directly accessible in unit tests, PowerMock permits us to navigate this challenge.
Illustration:
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Output:
Clarification:
The Java code above employs PowerMock’s Whitebox to access the private method add() within the Calculator class. The main() function creates an instance of the Calculator class and invokes add(5, 10), which outputs 15. This method call aids in testing private methods without...
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modifying the entire code.
Note: PowerMock is advantageous for testing private, static, and final functions. When utilizing it, one must ensure that both PowerMock and Mockito dependencies are included (this method requires the use of a Maven project).
Advantages and Disadvantages of Testing Private Methods, Fields, and Inner Classes in Java
Here are some significant advantages and disadvantages of these testing methodologies:
Advantages of Testing Private Methods, Fields, and Inner Classes
Guarantees Comprehensive Test Coverage:
Testing private methods, fields, and inner classes ensures that every segment of the code is included in the tests, even if they are not directly invoked by public methods.
Enhanced Debugging and Validation:
Testing private components allows for verification of the class's internal processes, aiding in the identification of bugs.
Increased Flexibility in Testing:
Methods such as reflection or PowerMock provide flexibility when testing code that is otherwise hard to reach.
Enhances Encapsulation:
It is possible to maintain private methods, fields, and inner classes to uphold a well-encapsulated design of the code.
Disadvantages of Testing Private Methods, Fields, and Inner Classes
Violates Encapsulation:
Accessing private methods and fields directly (using reflection or PowerMock) can compromise the principle of encapsulation, which contradicts the principles of OOP.
Increased Complexity:
Techniques like reflection or PowerMock add complexity to the code, as employing these requires additional steps in the implementation.
Performance Burden:
Approaches such as reflection or PowerMock can slow down the performance of the code, especially with extensive test suites. For instance, reflection tends to be slower than direct method calls, which results in sluggish testing.
Conclusion
The most effective way to test private methods in Java is through the public methods that utilize them, thereby ensuring encapsulation as well. If direct access to the class is required, techniques such as reflection, package-private access, inner classes, or PowerMock can be implemented.
If you wish to expand your knowledge about Java, you can check out our Java Course.
How to Test Private Methods, Fields, and Inner Classes in Java – FAQs
Q1. Is it possible to test private methods in Java?
Yes, private methods can be tested in Java utilizing techniques such as reflection, PowerMock, package-private access, or public methods that call them internally.
Q2. Is it essential to test private methods?
No, it isn't mandatory to test private methods consistently. Since private methods are internal to a class, they ought to be tested through the public methods that utilize them.
Q3. How can reflection be applied to test private elements?
Reflection permits dynamic access to private methods by using setAccessible(true).
Q4. Can a private method be invoked in a test class?
Yes, it is possible to invoke a private method in a test class.
Q5. Are constructors considered public or private?
By default, constructors are declared in the public section of the class.
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