Chapter 6

Question 1

What is a class?

Answer 1

It is the template that describes characteristics of similar objects; blueprint to create objects of that class

Question 2

What is an object?

Answer 2

it is an instance of its’ class

Question 3

What kind of entity is an object?

Answer 3

It is a run time entity that contains date and responds to messages.

Question 4

what is encapsulation?

Answer 4

combining data and behavior into a single software package

Question 5

name the three characteristics of objects

Answer 5

state, behavior, identity

Question 6

What is the state of an object?

Answer 6

instance variables

Question 7

What goes into the behavior of an object?

Answer 7

Methods! which define an object’s behavior in response to messages. there are two types: mutators and accessors

Question 8

What’s the difference between mutators and accessors?

Answer 8

mutators change an object’s state. accessors access the object’s state

Question 9

what does a computer’s memory hold during execution?

Answer 9

variables that refer to objects, class templates, and objects

Question 10

Objects appear and occupy memory when instantiated and disappear when no longer need, through a process called ______.

Answer 10

Garbage collection, which is the JVM’s automated method for removing unused objects.

Question 11

What else does the garbage collection do?

Answer 11

it also tracks whether objects are referenced by any variables.

Question 12

describe the client and server relationship

Answer 12

Client is the message sender, server is the message receiver. Client only needs to know the interface, server implements and supports the interface

Question 13

What is an interface?

Answer 13

list of methods

Question 14

What is information hiding?

Answer 14

server’s data requirements and methods implementation hidden from THE CLIENT

Question 15

Name the two types of visibility modifiers

Answer 15

private and public.

Question 16

Define the private visibility modifier

Answer 16

only accessible in the enclosing class

Question 17

Define the public visibility modifier

Answer 17

class is accessible to anyone

Question 18

generally, what type of visibility modifiers should instance variables be?

Answer 18

Private! instance variables should generally be private.

Question 19

What do constructors do?

Answer 19

• initialize a newly instantiated object’s instance variables.
• activated only by the keyword new

Question 20

What happens with default constructors and their parameters?

Answer 20

Empty parameter lists.

Question 21

Name the two fundamental data type categories

Answer 21

Primitive (int, double, boolean, char) and reference (all classes, the objects they create.)

Question 22

what is the null pointer exception?

Answer 22

to cause a variable to no longer point at any object; set it equal to null

Question 23

should we avoid null pointer exceptions?

Answer 23

yes!!! we really should avoid null pointer exceptions.

Question 24

true or false: constructors are used when creating an object AND updating or resetting values

Answer 24

FALSE! constructors are only used when creating an object, NOT updating or resetting values

Question 25

If the method returns no value, the return type should be ___.

Answer 25

if the method returns no value, the return type should be void

Question 26

What does a return stmt in a void method do?

Answer 26

Simply ends the method

Question 27

True or False: a method can have multiple return statements:

Answer 27

True! a method can have multiple return statements

Question 28

True or false: if a method has a return type, implementation must have at least one return statement that returns a value of that type.

Answer 28

True. if a method has a return type, implementation must have at least one return statement that returns a value of that type.

Question 29

What are formal parameters?

Answer 29

formal parameters are parameters listed in a method’s definition

Question 30

What are actual parameters?

Answer 30

values passed to a method when it is invoked

Question 31

what are helper methods?

Answer 31

used by another method to perform part of larger task.

Question 32

are helper methods usually public or private?

Answer 32

they are usually private: only methods already defined within the class need to use them

Question 33

Describe the characteristics of global variables:

Answer 33

1. they are declared inside a class but outside any method;
2. accessible to any method in the class
3. held in memory as long as the object is held in memory

Question 34

Describe the characteristics of local variables

Answer 34

1. they are only declared inside a method
2. accessible only within that method
3. once it’s already done its’ job, it disappears. gets replaced

Question 35

what is the scope of a variable?

Answer 35

the region where a variable can validly appear in lines of code. variables declared within any compound statement enclosed in braces have block scope.

Question 36

where is the scope only visible?

Answer 36

it is visible only within code enclosed by braces

Question 37

what is the scope of a local variable?

Answer 37

it is usable in the body of the method that declares it

Question 38

what is the lifetime of a variable?

Answer 38

the period when a variable can be used.

Question 39

what is the lifetime of a private instance variable?

Answer 39

they exist as long as the object exists