Chapter 1 Introduction to Object- Oriented Programming and Problem Solving.

Chapter 1Introduction to Object-

Oriented Programming andProblem Solving

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Knowledge Goals

• Understand what a computer program is• Know the three phases of the software life

cycle• Understand what an algorithm is• Learn what a high-level programming

language is• Understand the difference between machine

code and Bytecode

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Knowledge Goals

• Understand the compilation, execution, and interpretation processes

• Learn what the major components of a computer are and how they work together

• Understand the concept of an object in the context of computer problem solving

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Skills Goals

• List the basic stages involved in writing a computer application

• Distinguish between hardware and software• List the ways of structuring code in a Java

application• Name several problem-solving techniques• Choose an applicable problem-solving

technique• Identify the objects in a problem statement

How can you distinguish the knowledge goals from the skills goals?

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What is Programming?ComputerA programmable device that can store, retrieve, and process data Computer programmingThe process of specifying objects and the ways in which those objects interact to solve problemsProgrammingWriting out instructions for solving a problem or performing a task Computer programInstructions defining a set of objects and orchestrating their interactions to solve a problem

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How do we write a Program?

Water-fall

Model

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How do we write a program …

Problem-Solving Phase

• Understand (define) the problem and identify what the solution must do

• Specify the objects and their interactions to solve the problem

• Follow the steps exactly to see if the solution really does solve the problem

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How do we write a program …

Implementation Phase

• Translate the object specifications (the general solution) into a programming language

• Have the computer carry out the solution and check the results

What if the solution isn't correct?

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How do we write a program …

Maintenance Phase

• Use the program• Modify the program to meet changing

requirements, to enhance its functionality, or to correct any errors that show up in using it

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How do we write a program …

Can'twe

shortenthe

process?

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How can a computer work with objects?

Information

Any knowledge that can be communicated

Data

Information in a form that a computer can use

Object

A collection of data values and associated operations

How does all this fit together?

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How can a computer work with objects…

Data with

relatedoperationsrepresentsinformation

asobjects

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How can a computer work with objects…

Objects contain data and operations

Consider a Name object

What sort of data would this object contain?

What sort of operations might we need to manipulate the data?

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How can a computer work with objects…

Whatother

operationsmight

wewant

?

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Classes of Objects

What about multiple objects with the same properties?

Class

A specification of the representation of a particular kind of object, in terms of data and behavior (operations)

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Classes of Objects

Date class

data: month, day, year

operations: set and return month, day, year

Date object (an instance of a class)

June

23

2004

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What is an algorithm?

How are the operations specified?

Algorithm

Instructions for solving a problem in a finite amount of time using a finite amount of data

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What is an algorithm?Objects: Key, Transmission, Gas Pedal, Engine, Phone

1. Insert the key.2. Make sure the transmission is in Park (or Neutral).3. Depress the gas pedal.4. Turn the key to the start position.5. If the engine starts within six seconds, release the key.6. If the engine doesn’t start within six seconds, release the key and gas pedal, wait ten seconds, and repeat Steps 3 through 6, but not more than five times.7. If the car doesn’t start, phone your mechanic.

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What is an algorithm?

Once we have the algorithm, then what?

We translate the algorithm into statements in a programming language

Say again?

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What is a programming language?

Programming language

A set of rules, symbols and special words used to construct a computer program

Statements

Specific combinations of symbols and special words that are defined by a programming language to be complete units within a program; analogous to sentences in a human language

Code

Instructions for a computer that are written programming language

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What is a programming language?

There isno

singlewayto

implementan

algorithm

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What kind of instructions …

Computer

A programmable device that can store, retrieve, and process data

Implies

accept data, send data, perform arithmetic operations, perform logical operations

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What kind of instructions …

Control structures

Statements that organize the instructions that specify the behaviors of objects

- sequence- selection- repetition- subprograms- asynchronous

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What kind of instructions …

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What kind of instructions …

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Software Maintenance

Maintaining software accounts for the majority of its live cycle (i.e., old programs never die, they just get modified)

Where were you on January 1, 2000?

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Software Maintenance

Software maintenance tips-Check existing code-Make changes to a copy-Change related aspects to leave clean,

consistent code for next change- Keep backup copies

Software maintenance is not glamorousbut it is necessary!

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How It All Works

Machine language

The language, made up of binary-coded instructions, that is used directly by the computer

Assembly language

A low-level programming language in which a mnemonic represents each machine language instruction for a particular computer

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How It All Works

High-level language:

R1 = R3 + R5

R2 = R6 - R1

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How It All Works

Levelsof

abstraction

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Machine Language

• Is not portable

• Runs only on specific type of computer

• Is made up of binary-coded instructions (strings of 0s and 1s)

• Is the language that can be directly used by the computer

Why is portability important?

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Assembly Languages

• Are machine dependent and run on only one specific type of computer

• Are translated into machine code by assemblers

• Are made up of English-like abbreviations such as LOAD, STORE, or ADD

Better than machine language…

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High-Level Languages

• Are portable • Are translated into machine code by

compilers• Instructions are written in language similar to

natural language• Examples -- FORTRAN, COBOL, Pascal,

C, C++• Many are standardized by ISO/ANSI to

provide an official description of the language

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High-Level Languages

Source code

Instructions written in a high-level language

Object code

A machine language version derived from source code

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Portability

Compiler portability

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Java's Road to Portability

Bytecode

A standardized machine language into which Java source code is compiled

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High-Level Languages

Direct execution

The process by which a computer performs the actions specified in a machine-language program

Interpretation

The translation, while a program is running, of non-machine language instructions (such as Bytecode) into executable operations

Virtual machine

A program that makes one computer act like another

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High-Level Languages

Do you understand the differencebetween C++ & Java portability?

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What's inside the computer?

Can you

nameany

externaldevices

?

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What's inside the computer?

Memory unit

Internal data storage inside a computer, made up of an ordered sequence of addressable cells

Addressable?

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What's inside the computer?

Executes instructions

The Manager

Does operations

Holds data and instructions

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What's inside the computer?

Hardware

The physical components of a computer

Software

Computer programs; the set of all programs available on a computer

Clock

An electrical circuit that sends out a train of pulses to coordinate the actions of the computer's hardware components; its speed is measured in hertz (cycles per second)

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What is system software?User/computer interface

A connecting link that translates between the computer's internal representation of data and representations that humans are able to work with

Interactive system

A system that supports direct communication between the user and the computer

System software

The set of programs that simplifies the user/ communication interface

Operating system

Set of programs that manages all the computer's resources

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What is system software?

Seehow

itallfits

together?

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Problem Solving

Problem solving

The act of finding a solution to a perplexing, distressing, vexing, or unsettled question

How do you define problem solving?

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Problem Solving

How to Solve It: A New Aspect of Mathematical Method by George Polya

"How to solve it list" written within the context of mathematical problems

But the list is quite general

We can use it to solve computerrelated problems!

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Problem Solving

How do you solve problems?

Understand the problem

Devise a plan

Carry out the plan

Look back

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Problem-Solving Techniques

Ask questions!

-What do I know about the problem?

-What is the information that I have to process in order the find the solution?

-What does the solution look like?

-What sort of special cases exist?

-How will I recognize that I have found the solution?

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Problem-Solving Techniques

Never reinvent the wheel!

Similar problems come up again and again in different guises

A good programmer recognizes a task or subtask that has been solved before and plugs in the solution

Can you think of two similar problems?

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Problem-Solving Techniques

Look for familiar things

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Problem-Solving Techniques

Solve by analogy

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Problem-Solving Techniques

Means-end analysis

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Problem-Solving Techniques

Divide and conquer

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Problem-Solving Techniques

Building-block approach

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Problem-Solving Techniques

Merging solutions

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Problem-Solving Techniques

Object-Oriented Problem Solving Stages

- Brainstorm List all objects that might contribute to solution

- Filter Review the classes to find duplicates or remove unnecessary objects

-Responsibilities Determine the operations associated with a class of objects

-Collaborations Determine the interactions between classes

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Problem-Solving Techniques

- Attributes Determine the values defined by a class that are used to represent its objects

-Driver Write a program for creating the objects and coordinating their collaborations to solve the problem