Welcome to Introduction to Object-Oriented

Programming (OOP)

COSC 2321

Dr. Mircea Agapie Office: SCIENCE 213-C agapie@tarleton.edu

254-968-0792

Syllabus, textbook, etc.

In this class, we’re going to use C++, one of the three most successful (OO) languages

(The other two are Java and Python)

Source: http://blog.codeeval.com/codeevalblog/2015#.VdqgdE1759A=

Source: http://spectrum.ieee.org/computing/software/the-2015-top-ten-programming-languages

Source: http://redmonk.com/sogrady/2015/07/01/language-rankings-6-15/

Ch. 1: Introduction to Objects

The progress of abstraction

The fundamental problem of computer programming: traversing the gulf between “machine space” and “problem space”.

This is done with the help of abstraction(s).

Low-level languages are “too close” to the machine

http://www.chipsetc.com/gold-value-in-computer-chips.html https://en.wikipedia.org/wiki/Robot-assisted_surgery

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Pros? Cons?

Examples: all machine, assembly and procedural languages

Domain-specific languages are “too close” to the problem

http://www.chipsetc.com/gold-value-in-computer-chips.html https://en.wikipedia.org/wiki/Robot-assisted_surgeryP

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Pros? Cons?

Examples: Lisp, Prolog, VHDL, Matlab, VAL (programming language for robotics), etc.

OO languages are “in the middle”

http://www.chipsetc.com/gold-value-in-computer-chips.html https://en.wikipedia.org/wiki/Robot-assisted_surgery

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Very short history of C++

• 1970s: C is invented and becomes very popular• C is a procedural language, and, as real-life C

programs become large, it gets harder to write, maintain and debug them, esp. when they are developed by teams, rather than individual programmers. This is the problem of scalability.

• 1980s: C++ is invented and becomes very popular• C++ combines the procedural features of C with OO

features (from Simula and other languages) –classes, information hiding, inheritance, polymorphism – thus greatly improving scalability.

Let’s see how much C we remember

What is the net effect of running this program?

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Let’s see how much C we remember

Can you rewrite the if statement in a simpler form?

Hint: true and false are represented in C as 1 and 0, respectively.

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Can you rewrite the if statement in a simpler form?

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Let’s see how much C we remember

One of these programs will crash; which one, and why?

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Let’s see how much C we remember

Review/interview – style questions at

http://www.mycquiz.com/

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Although some (most) compilers agree in simple cases, they don’t agree in all cases; this is the meaning of undefined behavior.

Review/interview – style questions at

http://www.mycquiz.com/

Ongoing assignment: Answer/study/understand all 26

questions!

EOL1

QUIZ

Explain very briefly why OOLs are “better” than Procedural Languages at solving real-life problems. Why are they worse?

Alan Curtis Kay (born May 17, 1940) is an American computer scientist. He has been elected a Fellow of the American Academy of Arts and Sciences, the National Academy of Engineering, and the Royal Society of Arts. He is best known for his pioneering work on object-oriented programming and windowing graphical user interface design.

He was the inventor of Smalltalk, the first version of which, known as Smalltalk-71, was created by Kay in a few mornings on a bet that a programming language based on the idea of message passing inspired by Simula could be implemented in "a page of code."

[Source: Wikipedia]

Remember:

There are no “pure” OO languages. (Even Simula and Smalltalk have loops and decisions!)

C++ is no exception to this rule, being a mixture of procedural, OO, and functional features.C++ is a superset of C.

An object has an interface

In OO parlance, “class” means “type”

Simula-67 used the keyword class for the first time

The difference between built-in types and abstracttypes …

An OO programming system welcomes the new, abstract classes defined by the programmer, and gives them all the care and type-checking that it gives to built-in types.

An OO programming system welcomes the new, abstract classes defined by the programmer, and gives them all the care and type-checking that it gives to built-in types.

Wait a second – what’s the big deal? C also has abstract types, they are called ______________.

C also has abstract types, they are called arrays, structs and unions.

However, they are not handled the same as the simple, built-in types; for instance:• Structs and unions cannot be compared for equality.• Arrays cannot be compared for equality, nor assigned to

each other.

Once a class is established, you can make as many objects of that class as you likeObjects communicate through interfacesThe interface defines what actions are possible

This is an example of a black-box diagram …

… but what is inside the box?

The hidden implementation

Inside the box/object there must be:

• Data that defines the state of the object

• Code that is called to satisfy the requests of the interface.

In a pure OOL, both data and code are “hidden”; they together comprise the implementation.

New in C++

Why is hiding important in programming?

B/c it provides modularity, so we:

• Allow the users to work with a simpler, abstractview of the object

• Prevent the users from inadvertently messing-up the inner workings of the object

• Can later tweak/optimize the implementation w/o worrying about unwanted effects in other parts of the program

Hiding is a.k.a. separating the interface from the implementation

C++ uses three explicit keywords to set the boundaries in a class: public, private, protected.

Reusing the implementation

Composition

Aggregation

Association

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Owner classComponent

class

Of the 3 relations, only Composition is directly supported in C++

Composition example (not in text)

This is similar to nested structs!

Improved example (not in text)

These are similar to pointers to

structs!

In composition, when the owning

object is destroyed, so are the

component objects

The remainder of Lecture 2 is from Ch.2

QUIZ

1. When/where was the keyword class first used in a computer language?

2. In OOL, the _____________ of a class must be kept separate from the _______________.

3. The above concept is called ________ing the ______________.

4. What are the benefits of doing so?5. What technique for code reuse did we cover?

Owner classComponent

class

Reusing the interface: composition

Reusing the interface: inheritance

Another UML diagram!

This is called a type hierarchy

Another UML diagram!

“Casting the solution in the same terms as the problem is tremendously beneficial because you don’t need a lot of intermediate models to get from a description of the problem to a description of the solution. “

“With objects, the type hierarchy is the primary model, so you go directly from the description of the system in the real world to the description of the system in code.

Indeed, one of the difficulties people have with object-oriented design is that it’s too simple to get from the beginning to the end. A mind trained to look for complex solutions is often stumped by this simplicity at first.”

“With objects, the type hierarchy is the primary model, so you go directly from the description of the system in the real world to the description of the system in code.

Critical thinking: What is the unmentioned assumption in the quote above?

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“With objects, the type hierarchy is the primary model, so you go directly from the description of the system in the real world to the description of the system in code.

Critical thinking: What is the unmentioned assumption in the quote above?A: That the real-world system has a hierarchical structure in the first place!

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Examples of problems that are notmodeled well with type hierarchies

(or inheritance):

• Anything that involves time: cause/effect, transactions, sequencing, correlations, etc.

• Anything that involves large numbers of identical elements: brains, ant colonies, weather simulations, finite-element models, etc.

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When all you have is a hammer …

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After this warning, let’s recognize that many real-life systems/problems are

hierarchical – that’s one of the reasons OOP became successful!

How to differentiate the new, derived class from the original, base class?

A. Add more functions/methods

How to differentiate the new, derived class from the original, base class?

B. Change the behavior of an existing base-class function

We say that the base function is overriden. The base and derived functions of the same name are said to be polymorphic.

B. Change the behavior of an existing base-class function

How to differentiate the new, derived class from the original, base class?

C. Remove (delete)an existing base-class function There is no standard UML

diagram for this!

Creating and destroying objects

Source: Leo Ferres, Memory management in C: The heap and the stack

Staticstorage

Contains:• Local, static and constant

objects• Unitialized global objects

Contains:• Local auto objects

Originally it meant “Block Started by

Symbol”

Remember: In C (and C++) uninitialized static variables are initialized by default with 0.

Contains:• Objects allocated dynamically

Speed vs. flexibility

Fast to access, but inflexible - the number of objects and their types must be known at compile-time.

Slower to access, but flexible - the number of objects and their types are decided at run-time, with malloc/free in C, and new/delete in C++.

Lifetime of objectsCompiler has no knowledge of lifetime of dynamic objects, stored on heap → It’s the programmer’s responsibility to delete them.

“As an alternative, the environment can provide a feature called a garbage collector that automatically discovers when an object is no longer in use and destroys it.

[…] writing programs using a garbage collector is much more convenient, but it requires that all applications must be able to tolerate the existence of the GC and its overhead. This does not meet the design requirements of the C++ language and so it was not included, although third-party garbage collectors exist for C++.”

Java has built-in GC.

Exception handling: dealing with errors

In C, errors are handled through return codes from functions, e.g.:

C++ exception handling

In C++, an exception is an object that is “thrown” from the site of the error and can be “caught” by an appropriate exception handler designed to handle that particular type of error.

C++ exceptions are objects dynamically allocated from the heap.

Unlike C, the throwing is done automatically,

with minimal programming effort

Source: http://stackoverflow.com/questions/9670396/exception-handling-and-opening-a-file

Multiple exceptions can be caught from the

same try … catch block

Source: http://stackoverflow.com/questions/10650219/try-catch-exception-handling-c

Continue taking notes in your notebook!

--Analysis and design--The 5 phases of the design process--Extreme programming--Why C++ succeeds--Strategies for transition

Pair programming

• You will experiment with it in more advanced classes, like Software Engineering.

• In our class, teamwork is OK (recommended, actually!) when discussing problems, but all programming must be done individually!

EOL 3