3CSE2 understanding Java Abstract Classes 2024

What is an abstract class in Java?

• An abstract class in Java is a class that cannot be instantiated and may contain abstract methods that must be implemented by subclasses.

• An abstract class cannot have any fields or properties.

• An abstract class must contain only concrete methods.

• An abstract class can be instantiated directly.

How do you declare an abstract method?

• Declare an abstract method by using the 'virtual' keyword in a concrete class.

• Use the 'abstract' keyword in an abstract class to declare an abstract method.

• Use the 'final' keyword in a class to declare an abstract method.

• Abstract methods can be declared without any keywords in a regular class.

Can an abstract class have concrete methods?

• Yes, an abstract class can only have abstract methods.

• No, an abstract class cannot have any methods.

• Yes, an abstract class can have concrete methods.

• An abstract class can only contain static methods.

What is the purpose of dynamic method dispatch?

• To improve code readability and maintainability.

• To reduce memory usage in applications.

• To enforce strict type checking at compile time.

• The purpose of dynamic method dispatch is to support runtime method resolution and enable polymorphism in object-oriented programming.

Explain polymorphism in Java with an example.

• Animal myAnimal = new Animal(); myAnimal.sound(); // Outputs: Animal sound

• class Dog extends Animal { void makeSound() { System.out.println("Woof"); } }

• class Animal { void makeSound() { System.out.println("Sound"); } }

• Example: class Animal { void sound() { System.out.println("Animal sound"); } } class Dog extends Animal { void sound() { System.out.println("Bark"); } } class Cat extends Animal { void sound() { System.out.println("Meow"); } } Animal myDog = new Dog(); Animal myCat = new Cat(); myDog.sound(); // Outputs: Bark myCat.sound(); // Outputs: Meow

What happens if a subclass does not override an abstract method?

• The subclass cannot be instantiated.

• The subclass inherits the abstract method's implementation.

• The abstract method is automatically implemented.

• The subclass can be instantiated with default behavior.

How does method overriding differ from method overloading?

• Method overriding allows multiple methods with the same name in different classes.

• Method overriding is about redefining a method in a subclass, while method overloading is about having multiple methods with the same name but different signatures in the same class.

• Method overriding is used to create new methods in the same class.

• Method overloading is when a subclass inherits a method from its parent class.

Can you instantiate an abstract class directly?

• No, you cannot instantiate an abstract class directly.

• Yes, you can instantiate an abstract class directly.

• You can instantiate an abstract class if it has concrete methods.

• Abstract classes can be instantiated using a factory method.

What is the relationship between abstract classes and interfaces?

• Abstract classes can provide partial implementation and state, while interfaces define contracts without implementation.

• Abstract classes and interfaces are the same concept in programming.

• Interfaces can provide default implementations for methods.

• Abstract classes cannot have any methods defined.

How does dynamic method dispatch support runtime polymorphism?

• Dynamic method dispatch only works with static types and does not support polymorphism.

• Dynamic method dispatch is a compile-time feature that resolves method calls.

• Dynamic method dispatch supports runtime polymorphism by allowing method calls to be resolved at runtime based on the actual object type.

• Dynamic method dispatch requires explicit type casting for method resolution.