1. Object-Oriented Principles and Implementations

2. Agenda Evolution of software OO software elements Object instantiation
Run-time environment
Mapping to real-world
Object lifecycle

3. Evolution of Software Remember: form, function, style Paradigms
data, logic, paradigm
state, behavior, style
state: collection of all data values (e.g., at this time)
Paradigms
monolithic
modular
functional => ADTs => OO => componentware??

4. OO Software Elements: Objects
real life view:
person, place, thing, concept, event
OO view: instantiation of a class
storage view:
area of storage allocated to hold both the data for this object and its superclasses (its “state”), including all hidden data, and references to executable code the object can invoke/call
multiple objects of same class share executable code and static variables

5. OO Software Elements: Classes
real life view:
template, factory, pattern, IRS tax form
OO view:
abstraction of a kind of object
definition of services (methods) that can be performed
storage view:
one copy of all static variables per class, plus the storage to hold one copy of all method code, plus some overhead
no storage for object/instance state

6. Local Object Instantiation
two storage areas:
local reference to object
local storage for object’s state and methods
“new” is normally used
allocates local memory
object storage is released when:
object is no longer in use and garbage collector runs
program exits

7. Local Object Storage Temperature Class
Declaration: Temperature outside_temp;
Temperature Class
outside_temp
(2AF0)
(object reference is null)
private double fahr_value;
Storage allocation:
outside_temp = new Temperature(32.0);
public Temperature(double temp)
{fahr_value = temp;}
2AF0
3C320
Temperature() code
3C000
f_to_c() code
3C200
public static double f_to_c(double temp)
{return 9/5*(temp-32.0);}
getCelsius() code
3C300
3C320
32.0
public double getCelsius()
{return f_to_c(fahr_value);}
3C328
3C000
3C32C
3C200
3C330
3C300

8. Two Local Objects of Same Class
Temperature outside_temp
= new Temperature(32.0);
Temperature water_temp
= new Temperature(212.0);
2AF0
3C320
3C320
32.0
Temperature() code
3C000
2AF4
3C340
3C328
3C000
f_to_c() code
3C200
3C32C
3C200
getCelsius() code
3C300
3C330
3C300
3C340
212.0
3C348
3C000
3C34C
3C200
3C350
3C300

9. Shallow Object Copy Temperature outside_temp = new Temperature(32.0);
Temperature water_temp
= new Temperature(212.0);
Temperature a_temp
= outside_temp;
2AF0
3C320
3C320
32.0
Temperature() code
3C000
2AF4
3C340
3C328
3C000
f_to_c() code
3C200
2AF8
3C320
3C32C
3C200
getCelsius() code
3C300
3C330
3C300
3C340
212.0
3C348
3C000
3C34C
3C200
3C350
3C300

10. Remote Object Instantiation
four storage areas:
local reference to object (actually, for “stub”/proxy)
local storage for proxy and parameters
remote storage for remote proxy, parameters and return value/exception info
remote storage for object’s state and methods
“new” is not used
remote proxy causes “new” for remote object
foundation for most of EA infrastructure

11. Run-Time Environment loads/unloads classes schedules threads
allocates storage
runs garbage collection
interfaces with operating system

12. Mapping to Real World
enabled by from exposed state to exposed interface
handling large problems: desirable characteristics
object-orientation’s part in solving problems

13. Desirable Characteristics: Modularity
isolates functionality
serves as unit of decomposition
can be assigned as a work item
allows for a standard interface
speeds time to market by aiding problem partitioning
helps with understandability
thus maintainability and extensibility

14. Desirable Characteristics: Encapsulation
simplifies interface
promotes consistency
controls access
allows underlying data representation to change
aids maintainability

15. Desirable Characteristics: Abstraction
allows easier identification of reusable parts
saves work effort by closer mapping to problem
improves reliability by supporting reuse
makes changes easier to propagate
central, inherited concepts
saves development time by inheriting capability

16. Desirable Characteristics: Reuse
saves time
allows for purchase vs. roll-your-own
allows reaping benefits of accumulated experience from reused entity

17. Object Orientation and the Real World
Classes are generalizations and abstractions of real-world objects and their behaviors
examples: business concepts (Order), people (User), service provider (DatabaseInterface)
Objects are unique and have an identity
examples:
order[451] (instance of Order)
SaleClerk[“Jane Doe”] (instance of User)
inventory_db (instance of DatabaseInterface)

18. Bean Object Activation Activities
creation
create bean object but defer assigning storage for state
passivation
disassociate bean object from its state and save the state
removes bean object from memory
activation
loads bean object into memory
restores state and associates with bean object
removal
remove bean object from memory