AbstrctClassesInterfaces

Which of the following allows multiple inheritance in Java?

• Abstract classes

• Interfaces

• Both

• None

What happens if a class implements an interface but does not define all its methods?

• It will compile successfully.

• It must be declared abstract.

• It will throw a runtime exception.

• It will automatically inherit default implementations.

Which of the following is true about abstract classes in Java?

• They can be instantiated.

• They can have constructors.

• They cannot have any method implementations.

• They must be final.

abstract class Animal {

    abstract void makeSound();

    void sleep() {

        System.out.println("Sleeping...");

    }

}

class Dog extends Animal {

    void makeSound() {

        System.out.println("Bark");

    }

}

public class Main {

    public static void main(String[] args) {

        Animal a = new Dog();

        a.makeSound();

        a.sleep();

    }

}

• Bark

• Sleeping...

• Bark

  Sleeping...

• • Compilation Error

interface Flyable {

    void fly();

}

class Bird implements Flyable {

    public void fly() {

        System.out.println("Flying high!");

    }

}

• Bird must declare fly() as abstract.

• Bird must implement fly() method.

• Flyable can have a constructor.

• Flyable can have private instance variables.

abstract class Vehicle {

    abstract void start();

}

interface Electric {

    void charge();

}

class Tesla extends Vehicle implements Electric {

    void start() {

        System.out.println("Starting silently...");

    }

    public void charge() {

        System.out.println("Charging battery...");

    }

}

• Compilation Error

• Starting silently... Charging battery...

• Starting silently...

• Charging battery...

abstract class Shape {

    Shape() {

        System.out.println("Shape created");

    }

    abstract void draw();

}

class Circle extends Shape {

    void draw() {

        System.out.println("Drawing Circle");

    }

}

•  Only "Drawing Circle" is printed

• "Shape created" is printed

• Both messages are printed

• Compilation Error

True or False: A class can extend one abstract class and implement multiple interfaces simultaneously.

• True

• False

What is a main benefit of using interfaces?

• To allow a class to have multiple constructors.

• To provide a default implementation for all methods.

• To prevent a class from being subclassed.

• To hide implementation details and provide polymorphism.

Which of the following statements about abstract classes in Java is true?

• An abstract class cannot have a constructor.

• All methods in an abstract class must be abstract.

• An abstract class can contain both abstract and concrete methods.

• An abstract class can be instantiated directly.