1. Object Orientation Yaodong Bi, Ph.D. Department of Computer Sciences
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Object Orientation
Yaodong Bi, Ph.D.
Department of Computer Sciences
University of Scranton
August 8, 2018

2. Classes and objects for modeling
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Classes and objects for modeling
Classes
Real world concepts
Student, course, bicycle, etc
Objects
Instances of real word concepts
John Smith, Operating Systems, Mongoose Mountain S100, etc
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3. Classes and objects for modeling
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Classes and objects for modeling
“Customers
John
and
Susan
entered the
MakeMoney
bank
and were served by
teller
Andy.”
Classes
Objects:
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4. Classes and objects in software
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Classes and objects in software
Objects
Packaging both data and the procedures that operate on the data into one
Operations are the only way to change the data items – encapsulation
Classes
Template of objects of the same type
Write once and use many times
Implementation classes/objects
Some classes/objects do not match to concepts in the real world
List, stack, tree, queue – containers
Exception classes
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5. Attributes and operations
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Attributes and operations
Instance attributes (simply attributes)
Properties (internal state) of an object
Student: name, major, class, GPA
Course: title, # of credits, description
Each object has its own value for an attribute
Instance operations (simply operations)
Services of an object
Stack: push, pop, isEmpty, isFull
Encapsulation
Attributes (private and protected) are not accessible directly by client
Operations are used to read/write the values of attributes
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6. Attributes and Operations
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Attributes and Operations
Class attributes (static attributes)
Represent properties that can be applied to all objects of the same class
Only one value for each class attribute shared by all objects of the class
All accounts of the CheckingAccount class have the same interest rate
Can be accessed in both instance and class operations
Class operations (static operations)
Used to access class attributes
Cannot access instance attributes and operations
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7. Class member access modes
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Class member access modes
Public
Public attributes and public operations
Accessible to all clients or the world
Protected
Protected attributes and operations
Accessible to the class and its subclasses
Private
Private attributes and operations
Only accessible by the operations of the class
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8. Member access modes in Java
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Member access modes in Java
Specifier
Class
Package
Subclass
World
Private Y N
No Specifier
Protected
Public
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9. Abstract and concrete classes
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Abstract and concrete classes
Abstract classes
Define a common interface for its subclasses
Defer some or all of its implementation of operations to its subclasses
Cannot be instantiated
Concrete classes
That are not abstract classes
Can be instantiated
Concrete subclasses implement all the operations
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10. Interfaces Signature of an operation: Interface: Operation name
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Interfaces
Signature of an operation:
Operation name
Objects/classes it takes as parameters
Return value and type
Interface:
The set of signatures of related operations
Representing a capability or a set of services
A class may implement multiple interfaces
Its objects have more than one set of services
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11. Inheritance Specifies is-a or a-kind-of relationship
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Inheritance
Specifies is-a or a-kind-of relationship
Generalization and specialization
Superclasses and subclasses
Single and multiple inheritance
Class and interface inheritance
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12. Superclasses and subclasses
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Superclasses and subclasses
Superclass
Also called base class or parent class
All of its members are inherited by its subclasses
Subclasses
Also called child classes
Inherit all the properties of its superclasses
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13. Single and multiple inheritance
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Single and multiple inheritance
Single inheritance
A subclass cannot have more than one parent
Multiple inheritance
A subclass may have more than one parent
Java does not allow multiple inheritance
Java allows multiple interface inheritance
Through interface implementation
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14. Class inheritance lattice
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Class inheritance lattice
Person
SSN
Name
getSSN()
getName()
Faculty
office
getOffice()
Student
major
getMajor()
Staff
dept
getDept()
Graduate
PayRate
getPayRate()
Underg
PayRate
getPayRate()
FullTime
salary
getSalary()
PartTime
PayRate
getPayRate() TA
labs
getLabs()
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15. Implementation inheritance
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Implementation inheritance
Also called class inheritance
Define an object’s implementation in terms of another object’s implementation
Pure class inheritance in C++
Pure class inheritance in Java
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16. Pure class inheritance with C++
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Pure class inheritance with C++
Class BinaryTree {
getRoot() {;}
setRoot() {;}
leftTree() {;}
rightTree() {;} }
Class BinSearchTree: private BinaryTree {
insert() {;}
remove() {;}
find() {;} }
The operations of BinaryTree are not accessible/visible to the clients of BinSearchTree because BinaryTree is private
They use the operations of BinaryTree
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17. Pure class inheritance with Java
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Pure class inheritance with Java
Java does not allow private parent
The parent and grandparents are public and accessible through the subclass
Java cannot implement pure implementation inheritance.
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18. Interface inheritance
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Interface inheritance
Describe when an object can be used in place of another
Pure interface inheritance in C++
Superclasses are pure abstract classes
Pure interface inheritance in Java
Superclasses are Java interfaces
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19. Interface inheritance with C++
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Interface inheritance with C++
Class Stack {
virtual push() = 0;
virtual pop() = 0;
virtual isEmpty() = 0;
virtual isFull() = 0; }
A C++ Abstract class
Class MyStack: public Stack {
push() {;}
pop() {;}
isEmpty() {;}
isFull() {;} }
Class YourStack: public Stack {
push() {;}
pop() {;}
isEmpty() {;}
isFull() {;} }
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20. Interface inheritance with Java
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Interface inheritance with Java
Interface Stack {
push();
pop();
isEmpty();
isFull() 0; }
A Java Interface
Class MyStack implements Stack {
push() {;}
pop() {;}
isEmpty() {;}
isFull() {;} }
Class YourStack
implements Stack {
push() {;}
pop() {;}
isEmpty() {;}
isFull() {;} }
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Polymorphism
When a client sends a request to a reference, the method executed depends on the object behind the reference
Polymorphism and inheritance are very powerful tool in software design
So powerful that if they are used properly, they can hurt really bad
If something goes wrong, it is hard to tell which class/object caused the problem
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22. Dynamic (late) binding
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Dynamic (late) binding
Dynamic binding is a way of implementing polymorphism
It means that a function call is not linked to the actual function until execution time
Since a reference may be used to point to different types (subtypes or subclasses) of objects at execution time, so the actual function to be executed may not be known when the program is compiled.
The opposite of dynamic binding is static binding which links a function call to the actual function at compilation time.
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23. 8/8/2018
Method Overriding
A subclass overrides the operation(s) defined in the parent/grandparent classes.
This is for specialized subclasses to override the behavior defined in the super class(es).
For example:
Superclass Employee’s print method prints employee’s SSN, Name, Address.
Its subclass Engineer’s print method prints engineer’s type and level in addition to employee’s normal information.
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24. Function overloading The same name is used for more than one function
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Function overloading
The same name is used for more than one function
For example, a function of adding two integers may be named the same as the one of adding two floats:
Add(int x, int y);
Add(float x, float y);
Two functions use the same name for the same purpose with different data parameters
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25. Inheritance vs. Composition
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Inheritance vs. Composition
Two common techniques for reuse
Class Inheritance
White-box reuse
Defined at compile-time, statically
Cannot change parent at rum-time
Object Composition
Black-box reuse
A reference/pointer to the object
Can be changed at run-time
Favor composition over inheritance
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26. Delegation A receiving object delegates requests to its delegates
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Delegation
A way to make composition as powerful as class inheritance
A receiving object delegates requests to its delegates
== subclass defers request to parent class
In class inheritance
parent can use this to access the child
In delegation
Receiving object can pass itself to its delegate
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27. Three techniques for reuse
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Three techniques for reuse
Class Inheritance
can provide default operations and let subclass override them
Cannot be changed at run-time
Object Composition
Can change the behavior being composed at run-time
Requires redirection and so becomes less efficient
Generics
Changes the types that a class can use
Cannot change at run-time
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28. 8/8/2018
Nested Classes in Java
A class, nested class, that is defined in another class, enclosing class.
A nested class can be static and non-static
Static nested called static nested classes
Non-static class called inner classes
A nested class is a member of the enclosing class.
An inner class has an implicit reference to its enclosing class
A static nested class does NOT have any reference to its enclosing class
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29. 8/8/2018
Static Nested Classes
A static nested class (SNC) is associated with its enclosing class.
A SNC cannot refer to instance members of the enclosing class.
A SNC interacts with the instance members of its enclosing class and other classes just like any other top-level class
A SNC may be declared public, protected, private, and package private.
A SNC is behaviorally a top-level class.
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Inner Classes
An inner class is associated with an instance of its enclosing class.
It has direct access to that instance’s members, even private members.
An inner class CANNOT define any static members
An inner class CANNOT define static initializers
An inner class CANNOT define interfaces
An inner class may define static final compile-time constants
Two special kinds of inner classes
Local classes
Anonymous classes
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31. Local Classes A local class is a class that is defined in a block.
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Local Classes
A local class is a class that is defined in a block.
A block is a group of statements between two matching parenthesis.
A local class is typically defined in a method.
A local class has access to the members of its enclosing class
A local class can only access local variables in the block, that are declared final.
Since SE 8, it can access local variables that are final or effectively final
Effectively final – whose value is never changed after initialized.
Since SE 8, it can access the parameters of the method in which (as the block) the class is declared.
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32. Anonymous Classes An anonymous class is a local class without a name
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Anonymous Classes
An anonymous class is a local class without a name
You can only use it once
Anonymous classes are used only in expressions
Declaration components
The new operator
The name of an interface or a class to extend
Parentheses that contain the arguments to a constructor
A constructor of the class to extend
No arguments if it is an interface
A declaration body of the anonymous class
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33. 8/8/2018
Anonymous Classes
An anonymous class (AC) can access the members of the enclosing class
An AC can only access local variables what are final or effectively final
An AC cannot declare static members unless they are constant variables
An AC can declare:
Instance fields
Instance extra methods (not defined in the superclass)
They only be called inside the AC
Instance initializers
Local classes
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34. Static and Instance Initializers
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Static and Instance Initializers
A static initializer may be used to initialize static variables with complex logic, e.g., JDBC connection.
public class ClassWithStaticInitializer {
static { // statements of static initializer }
//other members }
A class may have any # of static initializers and they are executed in the order they appear in the class declaration
A class may define instance initializers that are executed before each constructor is executed.
public class ClassWithInstanceInitializer {
{ // statements of instance initializer }
//other members including constructors
Instance initializers will be called in the order they appear.
Instance initializers may be used to define common parts for all constructors of the class.
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35. Toolkits A set of predefined classes
Provides useful, general-purpose functionality
Collection classes (list, stack, etc)
GWT (Google Web Toolkit)
Does NOT impose any design level decision
Code Reuse
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36. Frameworks A reusable design for a type of applications
Dictates the architecture of your app
Overall structure
Key components and their responsibilities
How classes/objects interact with each other
Design reuse
Inversion of Control
Dependency Injection
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37. Frameworks Framework examples: Web Apps
J2EE, Spring Framework, .Net
ORM (object to relation mapping)
Hibernate, OpenJPA, MyBatis
Mobile Apps
Android
iOS
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