Chapter 5: Class Design

Question 1

How can Java support multiple inheritance?

Answer 1

Through the use of interfaces

Question 2

Does Java support multiple levels of inheritance?

Answer 2

Yes

Question 3

How can you prevent a class from being extended?

Answer 3

By using the ‘final’ keyword

Question 4

When extending a class without a no-argument constructor, what do you need to do?

Answer 4

Explicitly call super() with valid arguments for one of the super class’s constructors

Question 5

T or F. You can execute code in the constructor before calling super()

Answer 5

False

Question 6

Which is executed first? Parent or child constructor?

Answer 6

Parent

Question 7

How can you access parent members?

Answer 7

Both ‘this’ and ‘super’ will work for inherited members

Question 8

What are the requirements for overriding?

Answer 8

Must have the same signature
Child must be at least as accessible as the parent
Child may not throw a checked exception that is new or broader than one thrown by parent method
Return type must be same or subtype of parent return type

Question 9

T or F. A subclass can have a method with the same name as a private method in the parent class

Answer 9

True

Question 10

How can you explicitly call the parent’s version of an overridden method?

Answer 10

Using the ‘super’ keyword

Question 11

What is a hidden static method?

Answer 11

A static method that has been overridden. Both must be static

Question 12

Which version of a method is called if an overridden method is called on a child object in the parent class?

Answer 12

The child version

Question 13

Which version of a method is called if a hidden method is called on a child object in the parent class?

Answer 13

The parent version

Question 14

How do you prevent a static method from being hidden?

Answer 14

Make it ‘final’

Question 15

What are the rules for defining an abstract method?

Answer 15

No implementation is provided in the class where it’s declared
It cannot be final
It can only be defined in an abstract class or interface
It cannot be private

Question 16

What is a concrete class?

Answer 16

The first non-abstract class to extend an abstract class

Question 17

What must a concrete class do?

Answer 17

Must implement all inherited abstract methods

Question 18

What keyword is used when an interface inherits from another interface?

Answer 18

extends

Question 19

What keyword is used when an abstract class inherits from an interface?

Answer 19

implements

Question 20

What are variables assumed to be in an interface?

Answer 20

public static final

Question 21

What are methods assumed to be in an interface?

Answer 21

public abstract

-Unless they are static

Question 22

Can an interface be instantiated directly?

Answer 22

No

Question 23

Can an interface extend a concrete class?

Answer 23

No

Question 24

T or F. Static methods in interfaces are inherited by classes that implement the interface?

Answer 24

False

Question 25

How do you call a static method in an interface?

Answer 25

By using the name of the interface class

Question 26

T or F. You can’t implement two interfaces with the same method name

Answer 26

False. You can implement one of those methods to satisfy both interfaces

-Unless return types are different

Question 27

What is unique about default methods in comparison to other abstract methods?

Answer 27

They aren’t required to be implemented

They have a method body

Question 28

If you cast a reference variable to the parent type, can you still access subclass members?

Answer 28

No. You can only access members available to the reference type

Question 28

If you cast a reference variable to the parent type, can you still access subclass members?

Answer 28

No. You can only access members available to the reference type

Question 29

When you cast an object to a different type, is it’s type changed in memory?

Answer 29

No

Question 30

T or F. You must explicitly cast a subclass to superclass

Answer 30

False

Question 31

T or F. You don’t need to explicitly cast a superclass to a subclass

Answer 31

False

Question 32

T or F. You may cast to unrelated types

Answer 32

False

Question 33

What is a virtual method?

Answer 33

A method whose implementation isn’t determined until runtime