This document discusses key concepts of object-oriented programming including classes, interfaces, encapsulation, data hiding, delegation, fields, access modifiers, methods, constructors, static members, and the this keyword. It explains that classes define public interfaces and private implementations, and that encapsulation involves containing all class responsibilities. Fields hold class data, and access modifiers control visibility. Methods define behavior, and accessor/mutator methods are used to follow data hiding. Constructors initialize objects, and static members are shared among instances. The dot operator indicates class/object membership.

1. Classes and Class
Members
Chapter 3

2. 3
Public Interface
Contract between class and its clients
to fulfill certain responsibilities
The client is an object that calls methods
on another object or class.
The interface details what the class does,
but not how it does it.

3. 3
Private Implementation
The private implementation of a class
is the detailed explanation of how the
class does its work.
Clients do not know these details.

4. 3
Encapsulation
A good contract promises a well-
defined area of responsibility.
Each class should fully encapsulate
(contain) all its responsibilities.
What the class does should be clear but
the details of how it does it should be
hidden.

5. 3
What is data hiding?
Data hiding is a term used to indicate
that a class’s internal state is hidden
from its clients.

6. 3
Delegation
A class should fulfill and restrict itself
to one area of responsibility.
Classes should delegate outside
responsibilities to other classes.

7. 3
Class Fields
Class fields hold the class data. Each
field has a type:
Intrinsic Types
The Java language defines eight intrinsic types
Java Library Types
User-Defined Types
Classes defined by the programmer

8. 3
Public vs. Private Fields
The keywords public and private
are referred to as access modifiers.
Use private keyword to hide field from
clients.
Use public keyword to allow clients
access to field.

9. 3
Methods
Methods define the behavior of the
class.
Methods can return a value:
Return type can be an intrinsic type or an object.
Use the keyword void if a value is not to be returned by
the method.
Methods can accept parameters:
A parameter is an object you pass in to the method
when you call it.
Parameters follow the same naming conventions as
field names.

10. 3
Accessorand MutatorMethods
Accessor methods return information
Typically named to indicate that a value is being
returned:
getAge()
getAccountBalance()
Mutator methods modify the state of
the object.
Typically named to indicate that a value is being
changed:
setAge()
addDeposit()

11. 3
Why Use Accessors and Mutators?
Follows the concept of data hiding
Allows the class designer to change how
a method is implemented without
rewriting clients

12. 3
What is a constructor?
A constructor is a special method that
creates an instance of your class.

13. 3
Constructors
Constructors initialize objects with
valid values.
Constructors have special rules:
May accept parameters
Never marked with a return type
A default constructor:
Takes no parameters
Is provided by the compiler if you do not
provide one

14. 3
Static Members
Static members belong to the class
and are shared by all instances of the
class.
Declared using the static keyword
Can be accessed without an instance of
the class

15. 3
Dot Operator
The dot operator indicates that a
method or member field (right side of
dot) belongs to the object or class (left
side of dot).
ClassName.someStaticMemberField
ObjectName.someMethod()

16. 3
The this Keyword
Is a self-reference to the current object
Provided only in instance methods, not in
static methods