Java Class Design Flashcards

What is the key difference between overriding and hiding a method in Java?

Answer: Overriding applies to instance methods; hiding applies to static methods

Overriding uses dynamic dispatch for instance methods; static methods are hidden, meaning the reference type determines which version runs.

When can a subclass override a parent method with a narrower (more specific) return type?

Answer: When the return type is a subtype of the parent method's return type (covariant return)

Java allows covariant return types: the overriding method may return a subtype of the parent method's declared return type.

Which of the following access modifiers can be used on a top-level class declaration?

Answer: public or package-private only

Top-level classes can only be `public` or package-private (no modifier); `private` and `protected` are not allowed at the top level.

What is the purpose of the `@Override` annotation in Java?

Answer: It documents the intended override and lets the compiler catch signature mismatches

`@Override` tells the compiler to verify that this method actually overrides a superclass or interface method, catching typos or signature errors.

A local class declared inside a method can access which of the following from the enclosing method?

Answer: Only effectively final local variables

Local (and anonymous) classes can access local variables from the enclosing method only if they are effectively final.

Which of the following is NOT a valid use of the `this` keyword in Java?

Answer: Calling a static method on the current class

Static methods belong to the class and are not invoked via an instance reference like `this`; they are called on the class name.

What is an anonymous class in Java?

Answer: A class that is declared and instantiated in a single expression, usually extending a class or implementing an interface

An anonymous class is a local class without a name, declared and instantiated inline, typically to provide a one-off implementation.