introduction to object- oriented programming and problem...

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 dataComputer 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?

InformationAny knowledge that can be communicatedDataInformation in a form that a computer can useObjectA 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 objectWhat 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?

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

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Classes of ObjectsDate class

data: month, day, yearoperations: set and return month, day, year

Date object (an instance of a class)June232004

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What is an algorithm?

How are the operations specified?

AlgorithmInstructions 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 languageA set of rules, symbols and special words used to construct a computer programStatementsSpecific 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 languageCodeInstructions 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 …

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

Implies

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

What kind of instructions …

Computer can …• Input data from an input device and output

data to an output device• Store and retrieve data from in memory and

secondary storage• Transfer data • Perform arithmetic operations• Compare data values• Branch to a different sections of instruction

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What kind of instructions …

Control structuresStatements 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?

e.g., Y2K Problem

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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!

Binary Representation of Data

• Binary Number• Decimal Number• Hexadecimal Number

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How It All WorksMachine languageThe language, made up of binary-coded instructions, that is used directly by the computerAssembly languageA 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 codeInstructions written in a high-level languageObject codeA machine language version derived from source code

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Portability

Compiler portability

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Java's Road to Portability

BytecodeA standardized machine language into which Java source code is compiled

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High-Level LanguagesDirect executionThe process by which a computer performs the actions specified in a machine-language programInterpretationThe translation, while a program is running, of non-machine language instructions (such as Bytecode) into executable operationsVirtual machineA 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 unitInternal 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?HardwareThe physical components of a computerSoftwareComputer programs; the set of all programs available on a computerClockAn 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 interfaceA connecting link that translates between the computer's internal representation of data and representations that humans are able to work withInteractive systemA system that supports direct communication between the user and the computerSystem softwareThe set of programs that simplifies the user/ communication interfaceOperating systemSet 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 solvingThe 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 problemsBut 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 problemDevise a plan

Carry out the planLook 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 guisesA 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 TechniquesObject-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