Interfaces And Abstract Classes - Practice Test

[#176] In Java, can an abstract class have default methods with implementations?

(A) No, abstract classes cannot have default methods

(B) Only if the methods are marked as "private"

(C) Only if the methods are marked as "final"

(D) Yes, starting from Java 8, abstract classes can have default methods with implementations

Correct Answer

(D) Yes, starting from Java 8, abstract classes can have default methods with implementations

[#177] In Java, can an interface have private methods with implementations?

(A) Only if the methods are marked as "static"

(B) Only if the methods are marked as "final"

(C) Yes, starting from Java 9, interfaces can have private methods

(D) No, interfaces cannot have private methods

Correct Answer

(C) Yes, starting from Java 9, interfaces can have private methods

[#178] In Java, can an abstract class extend another class?

(A) No, abstract classes cannot extend other classes

(B) Yes, abstract classes can extend both abstract and concrete classes

(C) Only if the superclass is marked as "static"

(D) Only if the subclass is marked as "final"

Correct Answer

(B) Yes, abstract classes can extend both abstract and concrete classes

Explanation

Solution: In Java, abstract classes can extend both abstract and concrete classes. When an abstract class extends another class (whether abstract or concrete), it inherits the properties and methods of that class. An abstract class is allowed to inherit from a concrete class and can override or use the methods from the superclass. Option A is incorrect because abstract classes can extend other classes. Option C is incorrect since there is no requirement for the superclass to be marked as "static." Option D is incorrect as the subclass does not need to be marked "final" to extend a class.

[#179] What is the purpose of the "extends" keyword in Java?

(A) To mark a class as abstract

(B) To declare a method

(C) To implement an interface

(D) To create a subclass

Correct Answer

(D) To create a subclass

[#180] In Java, can an interface extend another interface?

(A) No, interfaces cannot extend other interfaces

(B) Only if both interfaces have the same methods

(C) Yes, an interface can extend multiple interfaces

(D) Only if the interface is marked as "private"

Correct Answer

(C) Yes, an interface can extend multiple interfaces

Interfaces And Abstract Classes - Study Mode

[#176] In Java, can an abstract class have default methods with implementations?

Correct Answer

[#177] In Java, can an interface have private methods with implementations?

Correct Answer

[#178] In Java, can an abstract class extend another class?

Correct Answer

Explanation

[#179] What is the purpose of the "extends" keyword in Java?

Correct Answer

[#180] In Java, can an interface extend another interface?

Correct Answer