Can a source file contain more than one class declaration?

• A. Yes, but only one can be public.
• B. No, only one class is allowed.
• C. Yes, multiple public classes can be declared.
• D. No, it must be a single class file.

Answer: (A)

A source file in Java can indeed contain multiple class declarations, but with the stipulation that only one of those classes can be marked as public. This is a fundamental aspect of Java's design, allowing for better organization and encapsulation of classes within the same source file.

When a class is declared as public, its name must match the filename, which enforces the rule that if there is a public class in the file, that specific class is the one intended to be accessed from outside its package. Any additional classes declared in that file can be package-private (the default access modifier) or have other access modifiers, but they cannot be public if there's already a public class present. This structure contributes to clarity in code organization and class access control within large applications.

The other choices do not correctly represent this behavior of Java source files. Only allowing one class is too restrictive, as Java supports multiple class declarations in one file. Stating that multiple public classes can be declared contradicts the rule about matching class names to filenames. Lastly, the assertion that a source file must contain a single class overlooks the flexibility Java provides for declaring multiple classes.