Advanced Class Design

Question 1

Which keyword must be used in a class declaration if any of its methods uses the abstract keyword?

Answer 1

abstract

Question 2

How do the contents of an abstract class differ from those of an interface?

Answer 2

An abstract class can contain implementation, while an interface cannot.

Question 3

Which name must an anonymous class reference to implement an interface or extend a class?

Answer 3

The name of the interface or class that the anonymous class implements or extends.

Question 4

Which method does the Enum class provide to retrieve an ordinal value for an enumeration constant?

Answer 4

ordinal

Question 5

Which restriction limits objects when using an abstract class?

Answer 5

An abstract class cannot be instantiated.

Question 6

Which restriction limits implementation when using a final class?

Answer 6

A final class cannot be extended.

Question 7

Which keyword is used to implement members of an interface?

Answer 7

implements

Question 8

Which method does the Enum class provide to iterate through enumeration constants?

Answer 8

values

Question 9

How do the contents of an abstract class differ from a concrete class?

Answer 9

An abstract class can contain abstract members, while a concrete class cannot.

Question 10

Which three modifiers are implicit for fields declared in an interface?

Answer 10

public static final

Question 11

Which keyword is used to implement abstract members of an abstract class?

Answer 11

extends

Question 12

Which keyword is used to inherit members from one interface to another interface?

Answer 12

extends

Question 13

Can a static field override a non-static field in a superclass?

Answer 13

Yes.
If the class declares a field with a certain name, then the declaration of that field is said to hide any and all accessible declarations of fields with the same name in superclasses, and superinterfaces of the class.

A hidden field can be accessed by using a qualified name if it is static, or by using a field access expression that contains the keyword super or a cast to a superclass type.

Question 14

Can a static method override a non-static method in a superclass?

Answer 14

No! Java only allows:

1. Overriding an instance method by an instance method and
2. Hiding a static method by a static method

Question 15

Can the abstract modifier be placed before the access modifier public as in:
abstract public class TestClass { }

Answer 15

yes

Question 16

Do Enum objects implement Comparable?

Answer 16

Yes.

Question 17

Can an abstract method be defined with access modifier private?

Answer 17

No

Question 18

Can an abstract method be defined with access modifier protected?

Answer 18

Yes

Question 19

What are the valid access modifier that can be used with an abstract method?

Answer 19

public protected

Question 20

What are the valid modifiers that can be used to define an abstract class?

Answer 20

Same as for a top level class: public abstract .

Question 21

What is the result of GPA.MID where GPA is an Enum class?

Answer 21

“MID” which is the value printed for the Name() method.

Question 22

Can abstract be used with a local innner class?

Answer 22

Yes.