Guided Notes Ch. 9 ADT and Modules

Ch. 10 Object-Oriented Programming

PHP support for OOP and Assignment 4

Term project proposal

C++ and Java Designer Video presenations

Review questions

OOP: Early History

• OOP languages began in the 1960s with Simula project (extend Algol60 for simulation) => Simiula67

• Simula67’s influence took 2 different directions:

• Abstract data type (classes)

• Object paradigm (program = a collection of interacting independent objects) => Smalltalk-80

OOP: Development

• Beginning in the mid-1980s, object-oriented programming => a language paradigm and a methodology for program design

• Extremely effective mechanism for promoting code reuse and modifiability => dominant paradigm for large software projects

Major concepts of OOP

• Address to 3 issues in software design:• Need to reuse software component as much as

possible

• Need to modify program behavior with minimal changes to existing code

• Need to maintain the independence of different components

• Abstract data type vs. OOP – improved solution to above design problems

Five Basic OOP Elements

• Extension of the data and/or operations

• Restriction of the data and/or operations (info hiding, encapsulation, protection)

• Redefinition of one of more of the operations

• Abstraction (abstract method)

• Polymorphism (overloading and overriding)

Code centric and data centric

• Procedure language (code centric) – code the application in functions/procedures using parameter passing sent in/out data. Function does the transformation – data and function separation

• OOP language (data centric) – objects, which represent their data internally, contain functionality called methods – data and behavior exist together less thinking and better organized

Terminology of OOP

• Encapsulation: the only code that changes an object’s data structure is in the class easier maintenance

• Inheritance: a way of defining a new class by saying that it’s like an existing class

Polymorphism

• An OO feature that gives us the ability to treat an object in a generic manner.

• Invoke a behavior on existing classes for any new classes with extension and leave the details and differences to the interpreter at run time

• Different classes can have different behaviors for the same operation (PHP book page 130 example: display())

Overloading and Overriding

• Overriding – fancy kind of polymorphism is resolved at runtime. It occurs when one class extends another, and the subclass has a method in the super-class. The reason for“fancy” is that you can’t tell until run time.

• Overloading – trivial kind of polymorphism, resolved by the compiler at compile time. Overloading allows several methods to have the same name, and the compiler will choose by matching on argument type

3 levels of Name Spaces

• Must put a $this -> keyword in front of the member name (differs from Java or C++ where is optional, $this keyword tells PHP the variable from the object’s name space)

• 3 levels of name spaces:– Lowest level for local variable inside functions or

methods

– Middle level for the members of an object

– Highest level for global variables

Abstract method

• A method contains no code and implementer of any possible subtypes must implement the behavior for that method

• Show PHP book Example page 131-132

• The class-function call operator – ClassName::functionName( );

(page 132 bottom)

PHP’s Limitations

• No static members (like a global variable but it is tied to class name space)

• No Destructors for PHP 4 (clean up when script is finished executing)

• No multiple inheritance

PHP for this week and Assignment 4

• PHP include files

• Language reference:• Classes and objects

• Control structures – include, require

• Chapter 5 of PHP book

Review Questions

• How Simula67 influenced programming language development?

• What are the 3 software design issues that motivate OOP development?

• What are the major difference between procedure oriented programming and object oriented programming?

• OOP terminology: Encapsulation, Inheritance, Polymorphism, abstract method