B3-8.2

Abstraction is:

• adding to a problem

• filtering out all irrelevant characteristics and unnecessary details

• finding characteristics

• looking for similarities

What is an abstract class?

• An abstract class is one without any child classes.

• An abstract class is any parent class with more than one child class.

• An abstract class is special class which can be a base class.

What is an abstract method?

• An abstract method is any method in an abstract class.

• An abstract method is a method which cannot be inherited.

• An abstract method is one without a body that is declared with the reserved word abstract.

• An abstract method is a method in the child class that overrids a parent method.

Can an abstract class define both abstract methods and non-abstract methods?

• No—it must have all one or the other.

• No—it must have all abstract methods.

• Yes—but the child classes do not inherit the abstract methods.

• Yes—the child classes inherit both.

Can an abstract parent class have non-abstract children?

• No—an abstract parent must have only abstract children.

• No—an abstract parent must have no children at all.

• Yes—all children of an abstract parent must be non-abstract.

• Yes—an abstract parent can have both abstract and non-abstract children.

Can an abstract method be defined in a non-abstract class?

• No—if a class defines an abstract method the class itself must be abstract.

• No—only classes are abstract, not methods.

• Yes—a method can be declared abstract in any parent as long as the child classes also declare it abstract.

• Yes—there is no restriction on where abstract methods can be defined.

What is polymorphism in Java?

• It is when a single variable is used with several different types of related objects at different places in a program.

• It is when a program uses several different types of objects, each with its own variable.

• It is when a single parent class has many child classes.

• It is when a class has several methods with the same name but different parameter types.

What is an advantage of polymorphism?

• The same program logic can be used with objects of several related types.

• Variables can be re-used in order to save memory.

• Constructing new objects from old objects of a similar type saves time.

• Polymorphism is a dangerous aspect of inheritance and should be avoided.

What is the output of this program ?

• 2 2

• 3 3

• Compilation Error

How many stars are printed?

• 7

• 3

• 4

• 5

• Infinite Loop