Classes and Objects (Head First Java - Ch. 2, 4, 10)

Question 1

Whats a primitive data type? give examples.

Answer 1

not considered objects or raw values and are stored directly on STACK.

byte, int, float, char, long, short, double, boolean

Question 2

How many classes in a file can be a public class?

Answer 2

Only one.

Question 3

Constructors are a special kind of method. What are three peculiarities?

Answer 3

A constructor must have the same name as the class itself.

Constructors do not have a return type, not even void.

Constructors are invoked using the new operator when an object is created. Constructors play the role of initializing objects.

Question 4

__ is a construct that defines objects of the same type

Answer 4

A class

Question 5

An object is an instance of a __

Answer 5

a class

Question 6

Which operator is used to create an object?

Answer 6

“new” operator

Question 7

You need ____ classes to create and use an object? Why?

Answer 7

two classes. One for the type of object you want to use. One to put your main() method in (tester class)

Question 8

What is the point of a tester class?

Answer 8

To create and access objects of your new class type. It will use the dot operator to access the methods and variables of the new objects

Question 9

How do we declare an object in the tester class (an instance of a class)? How do we access the variables method?

Answer 9

1. [Class name] [variable] = new Class name
2. [variable].[method]

method is made in other class

Question 10

What’s a parameter?

Answer 10

is a local variable, with a type and name, and can be used inside of the body of the method

Question 11

What is a return type?

Answer 11

the expected data type in return value for a method. A method could also have a void return type.

Question 12

Can a variables value change once passed into a method?

Answer 12

No - the value can only be changed within the method

Question 13

Is it required to have a return value for a non-void return type?

Answer 13

No it’s not require if we are just calling the method for the work it does inside the method

Question 14

What’s a setter method?

Answer 14

A method used just to set the value of an instance variable - it will have a void return type

Question 15

What’s a getter method?

Answer 15

A method used to return the value of an instance variable - it will have a matching return type

Question 16

What is encapsulation and whats it relation with setter methods?

Answer 16

Encapsulation is using setter methods to set boundaries for values. For example, a setter method can contain code to avoid negative values.

Question 17

instance variables should be ______

getters and setters should be ______

Answer 17

instance var should be private.

getters and setter should be public.

Question 18

What is the default value for an instance variable?

Answer 18

integers = 0
floating points = 0.0
booleans = false
references (String or objects) = null

Question 19

What’s the difference between a local and instance variable?

Answer 19

Instance variables are declared inside a CLASS, and has a default value

Local variables are declared within a METHOD, and don’t have a default value. They must be initialized.

Question 20

What can you not do with the Math class, but you can do with every other class?

Answer 20

We cannot create an instance of the class Math. (Can’t be instantiated) It is marked private.

Question 21

What is a static method?

Answer 21

a method part of a class rather than the instance of a class. No instance variables are required

Question 22

What happens if you try to use an instance variable in a static method?

Answer 22

Error. The static function won’t know which variable is being referred to

Question 23

What type of value is the same for ALL instances of classes?

Answer 23

Static variable. It will give you one value per CLASS, instead of one value per INSTANCE

Question 24

How do we make a variable a constant? (make it so a variable can’t be changed)

Answer 24

We can write:
public static final [var. type] [var. name]

static {
[var.name] = value;
}

Question 25

Constant “variable” names should be in _______.

Answer 25

ALL CAPS

Question 26

A final variable means _________

Answer 26

you can’t change its value

Question 27

A final method means _________

Answer 27

you can’t override the method

Question 28

A final class means _________

Answer 28

you can’t extend the class (can’t make a subclass)

Question 29

What is override?

Answer 29

When you have two methods with the same method name and the same parameters

Question 30

What is overloading?

Answer 30

When you have two methods with same method name, and different parameters