Interfaces

All methods in an interface are:

• private

• protected

• public abstract

• public final

In Java, interfaces can have:

• Static and default methods

• Constructors

• Private fields

• Synchronized methods

What happens if two interfaces define a constant int x = 10; and a class implements both?

• No problem, it's allowed

• Compilation error if accessed without qualification

• Runtime error

• x will take value from the first interface

What does the keyword instanceof check?

• Object reference equality

• Object memory location

• Whether an object is an instance of a class or interface

• Whether two classes are the same

What is the correct way to access a constant from an interface?

• x

• this.x

• InterfaceName.x

• new Interface().x

Which of the following is true?

• You can create an instance of an interface using new

• An interface can implement another interface

• Interfaces can have private methods

• A class can implement multiple interfaces

Who is the class user in software design?

• The one who extends a class

• The one who defines methods

• The one who calls/uses the class

• The one who inherits constants

What does the protected modifier mean?

• Accessible everywhere

• Accessible only inside the same package

• Accessible only in the class itself

• Accessible in the class and its subclasses

Which of the following correctly distinguishes aggregation vs inheritance?

• Aggregation is-is, Inheritance has-a

• Inheritance is-a, Aggregation has-a

• Both mean the same

• Aggregation is-a subclass

Which of the following are public, static, and final by default in an interface?

• Methods

• Fields

• Constructors

• Blocks