Understanding the Protected Method Access in Java: Anonymous Objects vs Named References

Explore the differences in accessing protected methods of anonymous objects versus named references in Java. Understand why certain compilations succeed or fail, and learn best practices around protected access.
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Understanding the Protected Method Access in Java: Anonymous Objects vs Named References

In Java, access to methods and variables is governed by access modifiers like public, protected, and private. This system helps define the visibility and accessibility of class members. One area that often generates confusion is how these access modifiers interact with anonymous classes and named references, particularly with protected methods.

The Problem: Accessing Protected Methods

Consider the following abstract class:

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In this code, whatever() is a protected abstract method, which means it can only be accessed within subclasses or classes in the same package. Now, let’s look at a scenario where we try to use this abstract class in another class called Three:

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Compilation Failure

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This error is expected because the reference one is of type One, and Java enforces the protected access rules.

The Solution: Using Anonymous Instances

Now, let’s modify the approach slightly and directly invoke the method using an anonymous instance of One:

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Why Does This Work?

In this case, the code compiles successfully because you are invoking whatever() on the anonymous class itself, not on a variable of type One.

Key Difference Explained

Named Reference: When you declare One one, your variable is treated as a reference of type One, which cannot access the protected whatever() method because it’s part of a different context, hence the compilation error.

Anonymous Class: By using new One(), you're directly accessing the method on the anonymous class instance. The compiler recognizes the context and provides the necessary access since you are accessing the method that belongs to the same instance.

Understanding Access Modifiers with Anonymous Classes

This behavior highlights an important aspect of Java's access control:

Even private members within anonymous classes can be accessed within their containing scope just like normal nested classes.

If an anonymous class has a public method, it can be accessed directly, whereas trying to access it through a reference of its parent class (like Object) will lead to errors unless that method is part of the parent's public contract.

Practical Examples

Here’s a practical demonstration:

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Conclusion

Understanding how protected method access works with anonymous objects versus named references in Java is crucial for writing effective and error-free code. By leveraging the capabilities of anonymous classes, you can access protected members in a manner that adheres to Java's access control rules. Always keep this difference in mind to avoid pitfalls in your Java programming journey!