Flashcard on OOPs Concepts

Front

What will be the output of the following code?
interface A {
void method();
}
abstract class B implements A {
public void method() {
System.out.println("Class B");
}
}
class C extends B {
}
public class Main {
public static void main(String[] args) {
C obj = new C();
obj.method();
}
}

Back

Class B

Front

What will be the output of the following code?
abstract class Animal { abstract void makeSound(); static 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) { Dog d = new Dog(); d.makeSound(); Animal.sleep(); } }

Back

Bark Sleeping...

Front

What will happen when the following code is executed?
interface A {
static void display() {
System.out.println("Interface A");
}
}
class B implements A {}
public class Main {
public static void main(String[] args) {
B obj = new B();
obj.display();
}
}
Options: A) Interface A, B) Compilation error, C) Runtime error, D) None of the above

Back

Compilation error

Front

What will be the output of the following code?
abstract class A { A() { System.out.println("Abstract class A constructor"); } } class B extends A { B() { System.out.println("Subclass B constructor"); } } public class Main { public static void main(String[] args) { B obj = new B(); } }

Back

Abstract class A constructor
Subclass B constructor

Front

Which of the following statements about abstract classes is FALSE?

Options: A) An abstract class can have final methods
, B) An abstract class can implement an interface
, C) An abstract class cannot have a constructor
, D) An abstract class can have static methods

Back

An abstract class cannot have a constructor

Front

What is the correct way to define multiple interface implementations?

Options: A) class A extends B, C {}
, B) class A implements B, C {}
, C) class A implements B extends C {}
, D) class A implements B & C {}

Back

class A implements B, C {}

Front

If a class implements multiple interfaces with methods having the same signature, what happens?

Back

The class must provide a single implementation for the method.

Front

If a class implements multiple interfaces with methods having the same signature, what happens?

Back

The class must provide a single implementation for the method.

Front

What happens when an interface method is declared static?

Back

It can be called using the interface name.

Front

What will happen if a class implements an interface but does not provide implementations for all methods?

Back

Compilation error and the class must be declared abstract.