Abstract Classes and Interfaces Flashcards

Is it correct that the class ABC is declared as abstract without any abstract methods?

Why does the class AbstractClass show a compilation error?

Which class is instantiable?

What must class B implement to avoid compilation errors?

What will be the value of the 'result' variable if the program runs correctly?

Can we write explicit constructors in an abstract class?

What is the error in the code where abstractMethod is private?

Can we declare protected methods in an interface?

What will be the output of the given abstract class program?

What will be the output of the program using class X and its subclass Y?

For every interface written in a Java file, a .class file will be generated after compilation.

What is the error in the code declaring a private field in an interface?

What will be the output of the code using interfaces and classes?

Can a class implement more than one interface?

What is causing the compile-time error in the implementation of interface X?

Does the code compile successfully when trying to change the value of the interface field?

Abstract Classes

An abstract class can be declared without any abstract methods; it can still provide complete method implementations.
A compilation error occurs if an abstract method contains a body; abstract methods must be declared without implementation.

Instantiation and Implementation

Only non-abstract classes can be instantiated; thus, Class B (subclass of abstract Class A) is instantiable.
When extending an abstract class, the subclass must implement all inherited abstract methods or also be declared abstract.

Between Abstract Classes and Interfaces

Abstract classes can contain constructors; they are not limited in the number of constructors they can define.
Abstract methods in an abstract class cannot be private; they must be accessible for implementation by subclasses.

Interfaces

Protected methods cannot be declared in interfaces; only public methods are permitted.
An interface generates a separate .class file after the compilation of each interface in Java.

Method Implementations

Interface methods must always be declared public; reducing visibility during implementation results in a compilation error.

Field Modifiers

Interface fields are inherently public, static, and final, meaning their values cannot be modified after initialization.
Declaring a private field in an interface is prohibited due to legal modifier restrictions.

Example Code Behavior

In the provided abstract class demonstration, calling methods results in the output: "FIRST", "THIRD", "SECOND" based on method chaining.
In another example, constructing an instance of Class Y from abstract Class X outputs "ONE", "TWO", and executing the abstract method outputs "THREE".

General Knowledge

A class can implement multiple interfaces, promoting polymorphism and code reusability.
Ensuring method signatures maintain public visibility when implementing interface methods is crucial to avoid compilation errors.

Test your knowledge about abstract classes and interfaces with these flashcards. Explore concepts like abstract methods, class declarations, and their implications in programming. Perfect for students learning Java or object-oriented programming.