What is the effect of implementing a public method on an ABAP class?

Implementing a public method in an ABAP class allows it to be accessed by other classes, thereby promoting modularity and reusability of code. Public methods are designated as accessible to any other class or program that has visibility of the class in which they reside. This means that anyone who creates an instance of the class or has access to the class can invoke its public methods, which is crucial for creating well-structured and accessible object-oriented designs.

The other options highlight different attributes related to ABAP class methods. For instance, a public method is not inherently restricted in terms of encapsulation—in fact, it is the designated means for interaction with the class's functionality. Moreover, public methods can indeed be overridden in subclasses, allowing for polymorphism, which is a fundamental principle in object-oriented programming. Lastly, the usability of a public method is not confined to the same program; it can be utilized across different programs as long as the necessary access rights and references are set up correctly.