programming and problem solving with java copyright 1999, james m. slack introduction what is a...

Programming and Problem SolvingWith Java

Copyright 1999, James M. Slack

IntroductionWhat is a Computer?Programming a ComputerTypes of Computer SystemsHistory of ComputersThe Software CrisisProgramming Languages

Programming and Problem Solving with Java 2

What is a Computer?Computer is a machine

Has partsRuns on electricityBreaks down sometimes

What makes it different from other machines?Can follow a list of instructions Instructions process symbols

Therefore

A computer isan information-processing

machine


What is a Computer?Computer follows a list of instructions one

instruction at a timeStart with first instructionDo each next instruction in turnStop when last instruction reached

Similar to how you follow a list of instructions...


What is a Computer?Example of following instructions - assemble a bike

Right Pedal1. Find the pedal with an "R" marked on the end of the threads.2. Insert the threads into the opening on the crank on the right side of the bicycle.3. Twist the threads into the crank by hand in a clockwise direction.4. Tighten the threads securely with a 5/8-inch open-end wrench.

Left PedalFollow the same assemblyinstructions for the right pedal (above) but twist the threads in a counterclockwise direction.

Pedal

Crank

Threads


What is a Computer?Kinds of instructions a computer can follow (in one

step) “Add the numbers 16 and 23”

Kinds of instructions a computer can’t follow (in one step) “Balance my checkbook”

What’s the difference?Computer instructions are simple (add 2 numbers,

subtract one number from another)Must combine thousands of computer instructions in a

program to do more complex tasks


What is a Computer?Kinds of computer instructions

Arithmetic: add, subtract, multiply, divideComparison: compare two numbers to see which is

greater, or whether the two numbers are equal or notBranching: jump to some other instruction in the

program (list of instructions) and continue processing from there

A computer can execute millions of these simple instructions each second


What is a Computer?Major parts of a computer

InputDevice

CentralProcess ing Unit

(CPU)

PrimaryMemory

OutputDevice

SecondaryMemory


What is a Computer?A vending machine

is like acomputer

M e m oryA m ount in s toc kA m ount of c hange

P roce ssin gChec k if in s toc kDeliver itemCom pute c hange

SnacksIn s e r tc o in s

M a k es e le c ti o n

C h a n g e

Inp ut de vice sCoin s lotS elec t ion buttons

O u tp ut de vice sChange s lotDelivery t ray


What is a Computer?Common input and output devices

Mon ito r( ou tpu t)

K e y bo ar d( inpu t)

Mo us e( inpu t)

S y s tem un it

Pr in te r( ou tpu t)


What is a Computer?Central Processing Unit (CPU)

Most important part of the computerFollows instructions

Important characteristicsClock speed

•How fast the computer switches between 2 on states or 2 off states•Early 80’s: 5,000,000 times per second (5 MHz)•Today: 400,000,000 to 1,000,000,000 and up! (400 MHz to 1 GHz)

Instruction set•The set of machine language instructions the CPU understands•Examples: Intel Pentium, Motorola PowerPC, IBM AS/400•Some CPUs understand machine language instructions of others -- AMD and Cyrix chips understand Intel Pentium instructions


What is a Computer?Subcomponents of a CPU

The arithmetic/logic unit, or ALU: does addition, subtraction, and other arithmetic operations, and also compares values

The control unit. determines which instruction to execute next

A small number of registers. each is a high-speed storage area for temporary results


What is a Computer?Types of Computer Memory

PrimarySecondary

Primary MemoryConnected directly to the CPUUsually called RAM (random-access memory)Usually loses contents when power switched off --

volatile


What is a Computer?Secondary Memory

Disks, tapes, floppy disks Is sometimes removableMuch cheaper than primary memorySlower than primary memoryKeeps contents when power switched off -- non-volatile

(a)

(b)


What is a Computer?Types of Computer Memory

Feature Primary Memory Secondary Memory

Speed (transfer rate) 10 to 200 megabytes/second 1 to 20 megabytes/second (harddisk)

Volatile (loses contentswithout power)

Yes No

Size Tens or hundreds ofmegabytes

Thousands of megabytes

Cost $2/megabyte $0.01/megabyte


What is a Computer?Primary Memory

Can imagine as sequence of cellsEach cell has a memory addressFirst cell is memory address 0

Memoryc e ll0

Memoryc e ll1

Memoryc e ll2



Each memory cell stores a single value, such as a small number

If you put a new value into a memory cell, the old contents is lost

2 1 0

(a) (b)

Memoryc ell

1002

Memoryc ell

1002

1 4 5 2 1 0



Can retrieve the contents of a cell without losing the contents

210(a) (b)

M e m o ryc e l l

1 0 0 2

M e m o ryc e l l

1 0 0 2

210210


What is a Computer?Secondary Memory

Information clustered in files File: collection of related

information Each file has a name Example: NAMES.DAT,

Balance.java

Files a re s to red inr ings c alled trac ks

Magneticrec ordings ur f ac e

Read/w r itehead


Programming a ComputerHow we solve most problems without a computer

Analyze the problem, come up with a solution

P roblemS tatem ent

P roblemS olution


Programming a ComputerHow we can get the

computer to solve a problem Must come up with

an algorithm (series of steps)

Computer follows the steps to solve the problem

P roblemS tatem ent

P roblemS olution

A lgorithmto s olveP roblem

(P rogram )


Programming a ComputerAlgorithm

Steps that a computer can follow to solve a problemHoliday Cookies1 cup sugar 1/4 tsp. ginger3/4 cup shortening 1 tsp. cinnamon1 cup dark corn syrup 1/2 tsp. nutmeg2 eggs 1/2 tsp. cloves1 lemon rind (grated) 2 tsp. anise seed3 cups flour 3/4 tsp. ground cardaman1 tsp. baking powder icing (powder sugar and water)1 tsp. baking soda colored sugar and candy decorations

1. Sift dry ingredients together in a large bowl and set aside.2. In another large bowl, use mixer to cream sugar and shortening together.3. Mix syrup, eggs, and lemon rind into sugar and shortening mixture.4. Add dry ingredients to mixture gradually.5. Refrigerate at least one hour to make handling easier.6. With rolling pin, roll out to 1/8-inch thickness on a floured surface, and cut with cookie cutters.7. Bake on greased cookie sheet 10-12 minutes at 375°F.8. Remove from cookie sheet and let cool to room temperature.9. Frost with icing, and decorate with colored sugar and candy.

Similar toa recipe


Programming a ComputerRecipe lists steps, but doesn’t say who is doing the

steps Implied that you (the cook) should do the stepsMany algorithms written this way -- structured approach

to programmingNew approach -- object-oriented programming

Consists of a set of cooperating objects trying to accomplish a goal

Each step says who (which object) should do that stepSimilar to the script for a play


Programming a ComputerTHE IMPORTANCE OF BEING EARNEST

by Oscar Wilde

The Persons of the Play

John Worthing, J.P. Lady BracknellAlgernon Moncrieff Hon. Gwendolen

FairfaxRev. Canon Chasuble, D.D. Cecily CardewMerriman, Butler Miss Prism,

GovernessLane, Manservant

The Scenes of the Play

Act I: Algernon Moncrieff's Flat in Half-Moon Street, W. Act II: The Garden at the Manor House, Woolton. Act III: Drawing-Room at the Manor House, Woolton


Programming a ComputerTHE IMPORTANCE OF BEING EARNEST (continued)

ACT ONESCENE. Morning-room in Algernon's flat in Half-Moon Street. The room is luxuriously and artistically furnished. The sound of a piano is heard in the adjoining room. (Lane is arranging afternoon tea on the table, and after the music has ceased, Algernon enters.) ALGERNON. Did you hear what I was playing, Lane? LANE. I didn't think it polite to listen, sir. ALGERNON. I'm sorry for that, for your sake. I don't play accurately-anyone can play accurately-but I play with wonderful expression. As far as the piano is concerned, sentiment is my forte. I keep science for life. LANE. Yes, sir. ALGERNON. And, speaking of the science of life, have you got the cucumber sandwiches cut for Lady Bracknell? LANE. Yes, sir. (Hands them on a salver.) ALGERNON. (Inspects them, takes two, and sits down on the sofa.) Oh! ... by the way, Lane, I see from your book that on Thursday night, when Lord Shoreman and Mr. Worthing were dining with me, eight bottles of champagne are entered as having been consumed. LANE. Yes, sir; eight bottles and a pint. ALGERNON. Why is it that at a bachelor's establishment the servants invariably drink the champagne? I ask merely for information.


Programming a ComputerTHE IMPORTANCE OF BEING EARNEST (continued)

LANE. I attribute it to the superior quality of the wine, sir. I have often observed that in married households the champagne is rarely of a first-rate brand. ALGERNON. Good Heavens! Is marriage so demoralizing as that? LANE. I believe it is a very unpleasant state, sir. I have had very little experience of it myself up to the present. I have only been married once. That was in consequence of a misunderstanding between myself and a young person. ALGERNON. (Languidly.) I don't know that I am much interested in your family life, Lane. LANE. No, sir; it is not a very interesting subject. I never think of it myself. ALGERNON. Very natural, I am sure. That will do, Lane, thank you. LANE. Thank you, sir. (Lane goes out.) ALGERNON. Lane's views on marriage seem somewhat lax. Really, if the lower orders don't set us a good example, what on earth is the use of them? They seem, as a class, to have absolutely no sense of moral responsibility. (Enter Lane.) LANE. Mr. Ernest Worthing. (Enter Jack. Lane goes out.)...


Programming a ComputerWhy is an object-oriented algorithm like a script?

Object-oriented algorithm simulates activities of several explicit actors

Each actor has specific steps to performEach actor free to use any appropriate technique to

accomplish its taskCombined effort of all these simulated actors results in

the goal of the algorithmCombined effort of real actors of a play results in

enjoyable entertainment


Programming a ComputerProgramming languages

Very formal language with strict rules about spelling and grammar

Need write algorithm in a programming language before running the algorithm on the computer

Many programming languagesWill use Java in this course


Programming a ComputerComputers understand machine language directly

Example: add 16 and 23 in Intel 8086 machine language1011 0000 0001 00000000 0100 0001 01111010 0010 0100 1000 0000 0000

1011 0000 0001 00000000 0100 0001 01111010 0010 0100 1000 0000 0000

OK ...


Programming a ComputerParts of machine language program step

First statement from example

Instruction says: Copy the number 16 into the AL register

Difficult to read and write machine language!

1011 0000 0001 0000

Copy informationto a register

Use theAL register

The number 16in binary (base 2)


Programming a ComputerAssembly language

One step up from machine languageEach assembly language instruction corresponds to one

machine language instruction

MOV AL,16D 1011 0000 0001 0000

ADD AL,23D 0000 0100 0001 0111

MOV [SUM],AL 1010 0010 0100 1000 0000 0000


Programming a ComputerAssembly language

Computer can’t understand assembly language directly

Must translate from assembly to machine language

Assembler: program that does this translation

MOV AL,16DADD AL,23DMOV [SUM],AL

Huh?

Ok ...

A s s embler1011 0000 0001 00000000 0100 0001 01111010 0010 0100 1000 0000 0000

MOV AL,16DADD AL,23DMOV [SUM],AL


Programming a ComputerHigh-level languages

Each high-level language instruction may correspond to several machine language instructions

Easier for people to read and write than assembly Java example:

(Note: Java usually translated to Java bytecodes, not Intel machine language...)

1011 0000 0001 0000

sum = 16 + 23; 0000 0100 0001 0111

1010 0010 0100 1000 0000 0000


Programming a ComputerHigh-level languages

Must translate high-level language program to machine language before computer can execute it

Compiler: program that does this translation

Ok ...

Compiler1011 0000 0001 00000000 0100 0001 01111010 0010 0100 1000 0000 0000

sum = 16 + 23;


Programming a Computer: JavaThe Java Programming Language

A high-level language Java compiler translates to Java bytecodes for execution

on a Java Virtual Machine (JVM)

Ok ...

J a va V i r tu a lM a c h in e

T ra n s la to r

1011 0000 0001 00000000 0100 0001 01111010 0010 0100 1000 0000 0000

sum = 16 + 23;J a va

C o m p i l e r

J V MM a c h in e

L a n g u a g e


Programming a Computer: JavaAdvantage of Java Virtual Machine approach

Can run compiled Java program on any machine with a Java Virtual Machine installed

Makes compiled Java programs very portableDisadvantage

Takes more time -- Java programs run slower than programs compiled to machine code

BUT ... Today’s machines are so fast that the difference is not

noticeable for many programs


Programming a Computer: JavaKinds of Java programs

ApplicationsApplets

ApplicationsRun as stand-alone programsPrograms stored on the same machine they run onLike a text editor, word processor, spreadsheet, ...Can be graphical or console-based

AppletsRun inside a web browserPrograms stored on a web server, run on a client

machine


Programming a Computer: JavaExample Java program (application)

// This Java program finds the sum of 16 and 23,// then displays the result.

public class Add16And23{ public static void main(String[] args) { int sum;

sum = 16 + 23; System.out.println("The sum of 16 and 23 is " + sum); }}

Steps to run this programType the program text exactlySave the program in file Add16And23.javaCompile the program with a Java compilerRun program Add16And23.class with a JVM interpreter


Programming a Computer: JavaUse an editor that saves text files, such as MS-

DOS edit (in MS-DOS box)


Programming a Computer: JavaCompile the program

javac Add16And23.java

Run the programjava Add16And23

Result: program should displayThe sum of 16 and 23 is 39

$ javac Add16And23.java$ java Add16And23The sum of 16 and 23 is 39$

Unix display


Programming: DevelopmentExample program: display average of seriesFirst step: understand the problem

Where should program get the numbers? KeyboardHow does program know how many numbers? Will enter

0 at end of listWhere should program display result? On screen

Second step: come up with algorithmSolve problem yourself -- write down steps you tookResult is an algorithm


Programming: DevelopmentSteps for

finding average of series of numbers

StepNumber Action

Value ofinputdata

Value ofrunning

total

Value ofrunningcount

Value ofaverage

1 Set running total to 0 — 0 — —

2 Set running count to 0 — 0 0 —

3 Read a value 9 0 0 —

4 Check if value is 0 (stop reading if so) 9 0 0 —

5 Add value to running total 9 9 0 —

6 Add 1 to running count 9 9 1 —

7 Read a value 3.2 9 1 —

8 Check if value is 0 (stop reading if so) 3.2 9 1 —

9 Add value to running total 3.2 12.2 1 —

10 Add 1 to running count 3.2 12.2 2 —

11 Read a value 8 12.2 2 —

12 Check if value is 0 (stop reading if so) 8 12.2 2 —

13 Add value to running total 8 20.2 2 —

14 Add 1 to running count 8 20.2 3 —

15 Read a value 0 20.2 3 —

16 Check if value is 0 (stop reading if so) 0 20.2 3 —

17 Stop , because value is 0 0 20.2 3 —

18 Compute the average by dividing therunning total by the count

0 20.2 3 6.73

19 Display the average 0 20.2 3 6.73


Programming: DevelopmentConvert steps into an algorithm

Display the program's titleSet running total to 0.Set running count to 0.Repeat these steps:

•Read a value.•Check if value is 0 (stop this loop if so).•Add value to running total.•Add 1 to running count.

Compute the average by dividing the running total by the count.

Display the average.


Programming: DevelopmentConvert algorithm into program

// This program displays the average of a series of// numbers terminated by zero. The user enters the numbers using// the keyboard, and the average is displayed on the screen.

import java.io.*;import java.text.NumberFormat;

public class ComputeAverage{ public static void main(String[] args) throws java.io.IOException, java.text.ParseException { double inputValue; // Last value read from the user double runningTotal; // Total of all input values read so far int runningCount; // Count of all input values read so far double average; // Average of input values

// Create an input stream and attach it to the standard // input stream BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in));

// Create a number formatter object NumberFormat formatter = NumberFormat.getInstance();

// Display the program title System.out.println("--- Compute Average ---");

// Set running total to 0 runningTotal = 0;


Programming: Development // Set running count to 0 runningCount = 0;

// Read the first input value System.out.print("Enter a value (0 to stop): "); System.out.flush(); inputValue = formatter.parse(inStream.readLine()).doubleValue();

// Keep reading until 0 while (inputValue != 0) { // Add value to running total runningTotal = runningTotal + inputValue;

// Add 1 to running count runningCount = runningCount + 1;

// Read the next input value System.out.print("Enter a value (0 to stop): "); System.out.flush(); inputValue = formatter.parse(inStream.readLine()).doubleValue(); }

// Compute the average average = runningTotal / runningCount;

// Display the average System.out.println("The average is " + average); }}


Programming: DevelopmentLast step: Make sure the program works correctly

First test -- ok--- Compute Average ---Enter a value (0 to stop): 9Enter a value (0 to stop): 3.2Enter a value (0 to stop): 8Enter a value (0 to stop): 0The average is 6.73333

Second test -- ok--- Compute Average ---Enter a value (0 to stop): 9.1Enter a value (0 to stop): 2.6Enter a value (0 to stop): 7.3Enter a value (0 to stop): 1.4Enter a value (0 to stop): 6.44Enter a value (0 to stop): 8Enter a value (0 to stop): 5.72Enter a value (0 to stop): 0The average is 5.79429

Third test -- not ok (doesn’t work if nothing to average)--- Compute Average ---Enter a value (0 to stop): 0The average is NaN


Programming: DevelopmentModified program

// This program displays the average of a series of// numbers terminated by zero. The user enters the numbers using// the keyboard, and the average is displayed on the screen.

import java.io.*;import java.text.NumberFormat;

public class ComputeAverage{ public static void main(String[] args) throws java.io.IOException, java.text.ParseException { double inputValue; // Last value read from the user double runningTotal; // Total of all input values read so far int runningCount; // Count of all input values read so far double average; // Average of input values

// Create an input stream and attach it to the standard // input stream BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in));

// Create a number formatter object NumberFormat formatter = NumberFormat.getInstance();

// Display the program title System.out.println("--- Compute Average ---");

// Set running total to 0 runningTotal = 0;


Programming: Development // Set running count to 0 runningCount = 0;

// Read the first input value System.out.print("Enter a value (0 to stop): "); System.out.flush(); inputValue = formatter.parse(inStream.readLine()).doubleValue();

// Keep reading until 0 while (inputValue != 0) { // Add value to running total runningTotal = runningTotal + inputValue;

// Add 1 to running count runningCount = runningCount + 1;

// Read the next input value System.out.print("Enter a value (0 to stop): "); System.out.flush(); inputValue = formatter.parse(inStream.readLine()).doubleValue(); }

if (runningCount > 0) {

// Compute the average average = runningTotal / runningCount;

// Display the average System.out.println("The average is " + average); }

else System.out.println("Can't compute average: No input values");

}}

Changes


Programming: DevelopmentLast step: Test program again

First test -- ok--- Compute Average ---Enter a value (0 to stop): 9Enter a value (0 to stop): 3.2Enter a value (0 to stop): 8Enter a value (0 to stop): 0The average is 6.73333

Second test -- ok--- Compute Average ---Enter a value (0 to stop): 9.1Enter a value (0 to stop): 2.6Enter a value (0 to stop): 7.3Enter a value (0 to stop): 1.4Enter a value (0 to stop): 6.44Enter a value (0 to stop): 8Enter a value (0 to stop): 5.72Enter a value (0 to stop): 0The average is 5.79429

Third test -- ok--- Compute Average ---Enter a value (0 to stop): 0Can't compute average: No input values


Programming: DevelopmentSteps in program development

Understand the problemCome up with an algorithmWrite the programTest the program


Programming: DevelopmentUnderstand the problem

Need to understand problem thoroughly before beginning to write program

Tempting to start writing program before understanding problem -- probably single most common cause of errors in programs

How to understand the problemLook at input and output requirementsAsk people involved with the problem domainTry writing about the program -- write what it should do in

your own words


Programming: DevelopmentCome up with an algorithmAlgorithm is a series of steps, and it ...

is finite -- can’t have infinite series of steps is unambiguous -- must state precisely what to do at

each step is effective -- must do what it is supposed to towill terminate -- won’t go on forever


Programming: DevelopmentWrite the program

If you have an algorithm this step is mechanicalGets easier the more you learn and use Java

Desk checkingSimulate the action of the

computer in your mindGood time to do this is as

you write the program (you’re thinking about the program anyway)


Programming: DevelopmentTest the program

Try the program with sample dataMake sure to try several different samples (may work on

one set but not others)Don’t worry if it doesn’t work the first time -- professionals

rarely get it right the first time, either


Types of ComputersFour major types of computer systems

Single-user personal computerTime-sharing computerBatch computerNetwork computer system


Types of ComputersSingle-user personal computer

One person uses at a timeHas become popular since early 80’s Interactive -- computer responds

immediately to user commands


Types of ComputersTime-sharing computer

Many people can use simultaneouslyEach person uses a terminal

connected to the computer

Printer

Min ic omputer


Types of ComputersHow does time-sharing computer service many

people simultaneously?Only appears to act this wayActually does a little bit of work for each person in turnProcess is called pollingPolls so fast that it seems like the computer is serving

everyone at the same time


Types of ComputersBatch computer system

Not interactive -- must schedule work with computer operator

Operator schedules work so the computer can get the most work done in the shortest time

Advantage of batch: efficiencyUsed in large companies for repetitive tasks

Payroll, accounting, ...

Mainf ramePr inte r


Types of ComputersComputer network

Group of connected computersServer: fast, expensive computer that stores programs

and other files for the other computers (clients)Advantage of network vs. time-sharing

Each client is a computerResponse time is better

Des ktop c omputer Des ktop c omputer

Des ktop c omputer Des ktop c omputer

Dis k A rray Serv er

Pr inter


History of ComputersAbacus: oldest mechanical calculating aid

Invented in Babylon about 3000 years agoAlso used by ChineseEach wire represents a decimal position (ones, tens, ...)Can do addition, subtraction, multiplication and division

by moving beads on the strings


History of ComputersBlaise Pascal

Invented first mechanical calculator in 1642Did multiplication and division

Gottfried von LeibnitzExpanded Pascal's machine in 1671Handled multiplication, division, and square roots

Joseph-Marie Jacquard Invented loom that read tape of punched cards in 1801Wove cloth according to instructions on cardsFirst machine that could be reprogrammed


History of ComputersCharles Babbage

Designed Difference Engine (mid 1800’s)Supposed to compute and print mathematical tablesNever completed -- Babbage spent time designing

Analytical EngineDesigned to follow instructions in a program and thus

handle any computationWould store program on cards in the machine's memory --

this is the stored program conceptNever completed -- English government stopped the

fundingProbably wouldn’t have worked -- required metalworking

skills beyond what was possible at the time


History of ComputersAugusta Ada (later Countess of Lovelace)

World’s first computer programmerAssisted BabbageTranslated one of Babbage’s papers on Analytical Engine

from French to English (1842) In margins, she wrote examples of how to use the

machine -- program examples


History of ComputersHerman Hollerith

Invented method of using punched cards for automated data processing

US government used Hollerith's machines to tabulate the 1890 census

Hollerith's firm later merged with three other firms to become International Business Machines (IBM)

Punched cards used for tabulating and sorting information into the 1960's


History of ComputersHoward Aiken

Designed the Mark I computer -- the world's first automatic computer (1944)

Operated with electro-mechanical switchesAble to multiply two numbers together in six seconds

John W. Mauchly and J. Presper EckertDesigned ENIAC -- the first general-purpose electronic

computer (1946)Hundreds of times faster than any electro-mechanical

computing deviceProgrammed by plugging wires into holes along the

outside of the machine.


History of ComputersFirst generation computers (1950’s)

UNIVAC I (1951, Sperry-Rand): first commercial computer

Other companies soon followedComputers were bulky, unreliableUsed vacuum tubes for electronic switching (hot --

burned out often)Most programs

written in machine language

Used punched cards for data storage

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History of ComputersSecond generation computers (late 50’s -

mid 60’s)Started using transistors instead of vacuum

tubesComputers became more reliableFirst high-level languages (FORTRAN, COBOL,

Algol)Larger primary memoryMagnetic tapes used for long-term data storage


History of ComputersThird generation computers (mid 60’s to

early 70’s) IBM introduced System 360 line: every

machine in the line could run the same programs

Integrated circuits used: contains many transistors

Most computers ran in batch mode


History of ComputersFourth generation computers (early 70’s on)

Very large scale integration: hundreds, thousands, or millions of transistors on a single chip

Computers have become inexpensive and reliableTime-sharing popular in 1970’s and 1980’sToday, single-user personal computers are popularThe Internet connects many computers in a world-wide

computer network


Software CrisisHardware vs. software

Hardware: physical parts of the computerSoftware: computer programs

Advances in hardware have been spectacularFast, affordable computer systemsComputers in everyday appliances

Advances in softwareHave been many significant advances (high-level

languages, compilers, object-oriented programming, modern design techniques, ...)

Still need to do more though...


Software CrisisToday, many programs are

Expensive: they cost much more than initial projectionsUnreliable: they have serious errors which cause them

to work incorrectlyLate: they are delivered months or years after they're

promisedThis is a crisis ...


Software CrisisAbstraction

Ignore details, concentrate on essential featuresMost powerful tool to solve the software crisis

Levels of abstractionSometimes, details at one level become essential

features at another levelExample: stereo

•Consumer level: concentrate on tuner, CD player, tape desk, speakers, amplifier•Stereo designer: concentrate on circuits,discrete parts, chips•Chip designer: concentrate on circuitswithin the chip


Software CrisisUse abstraction when writing computer program

Programmer gives a name to each part of the programWhen working within the part, programmer concentrates

on the steps within that partWhen working outside the part, programmer thinks of the

part by its name (ignores the steps within)Usually several levels of abstraction in a computer

programMethod: most detailed levelClass: consists of several methods (and other things...)Package: consists of several classesSystem of packages: consists of several packages


Programming LanguagesHundreds of high-level programming languages

No best programming language for all usesSome are better than others for certain uses

Four major groupsProceduralFunctionalLogicObject-oriented


Languages: ProceduralProcedural languages

Largest group of languagesAlso called imperative languagesProgram consists of list of statements

VariablesProgram stores temporary values in variables, and can

change the value of a variableDifferent from mathematics: once we have chosen the

value of a variable, it remains fixed throughout the expression

x y / 3


Languages: ProceduralBASIC (Beginner’s All-purpose Symbolic Instruction

Code) Popular language for beginnersSimple syntax (originally only 14 statement types)Can run on small computersExample

10 REM THIS BASIC PROGRAM FINDS THE SUM OF20 REM 16 AND 23, THEN DISPLAYS THE RESULT.30 LET SUM = 16 + 2340 PRINT "The sum of 16 and 23 is ", SUM50 END

Microsoft Visual BASICMuch more sophisticated version of BASICFull-fledged development system for Microsoft Windows


Languages: ProceduralCOBOL (COmmon Business Oriented Language)

Most commonly used language in businessDesigned for ease of data movementExample

IDENTIFICATION DIVISION. PROGRAM-ID. ADDNUMS. AUTHOR. SLACK. DATE-WRITTEN. JUL 11,1997. DATE-COMPILED. JUL 12,1997.* THIS COBOL PROGRAM FINDS THE SUM* OF 16 AND 23, THEN DISPLAYS THE RESULT. ENVIRONMENT DIVISION. CONFIGURATION SECTION. SOURCE-COMPUTER. IBM-370. OBJECT-COMPUTER. IBM-370. DATA DIVISION. WORKING-STORAGE SECTION. 77 TOTAL PICTURE 99. PROCEDURE DIVISION. ADD 16, 23 GIVING TOTAL. DISPLAY 'THE SUM OF 16 AND 23 IS ', TOTAL UPON CONSOLE. STOP RUN.END PROGRAM


Languages: ProceduralFORTRAN (FORmula TRANslator)

The first high-level languagePopular with scientists and engineers (although many

engineers are switching to C and C++ today)Example

PROGRAM ADDNUMSC THIS FORTRAN PROGRAM FINDS THE SUM OFC 16 AND 23, THEN DISPLAYS THE RESULT.

INTEGER SUM SUM = 16 + 23 WRITE (*, 10) SUM 10 FORMAT ('THE SUM OF 16 AND 23 IS ', I2) STOP END


Languages: ProceduralC

Popular with programmers who write system-level code (operating systems, compilers, ...)

Example/* This C program finds the sum of 16 and 23, then displays the result. */

#include <stdio.h>

void main(void){ int sum; sum = 16 + 23; printf("The sum of 16 and 23 is %d\n", sum);}


Languages: ProceduralPascal (named after Blaise Pascal)

Designed as a simple alternative to Algol (another early programming language)

Used extensively to teach programming until the early 1990’s

ExamplePROGRAM AddNums (Input, Output);

{ This Pascal program finds the sum of 16 and 23, then displays the result. }

VAR Sum : Integer;

BEGIN Sum := 16 + 23; writeLn ('The sum of 16 and 23 is ', Sum)END.


Languages: FunctionalFunctional languages

Based on mathematical functionsProgram consists of functions and function callsNo variables in a pure functional language

LispMost popular functional languageUsed widely in artificial intelligence (especially in the US)Example

; This Lisp program finds the; sum of 23 and 16, then displays the result.(progn (let (Sum) (setq Sum (+ 23 16)) (princ "The sum of 23 and 16 is ") (princ Sum) ))


Languages: LogicLogic languages

Based on formal rules of logic and inferenceOnce set, program can't change value of a variableProgram consists of a set of known facts, plus rules for

inferring new facts from the existing facts


Languages: LogicProlog

Most popular logic languageUsed widely in artificial intelligence (especially in Europe

and Japan)Example

/* This Prolog program finds the sum of 16 and 23, then displays the result. */

run :- Sum is 16 + 23, write ("The sum of 16 and 23 is ", Sum), nl.


Languages: LogicAnother example of Prolog

/* Shows Prolog's inference ability */

likes(tom, pizza).likes(tom, apple).likes(jill, taco).likes(jill, apple).likes(bob, beans).likes(bob, apple).likes(jody, Food) :- likes(jill, Food), likes(bob, Food).

Run program by writing a queryExample

Goal: likes(jill, Food)Food=tacoFood=apple2 Solutions

Can also infer solutions based on known factsGoal: likes(jody, Food)Food=apple1 Solution


Languages: Object-orientedObject-oriented languages

Model each real-world entity as an objectEach object has set of values and behaviorsEach object is therefore active, because it has behaviors

Simula (Simulation language)First object-oriented language (1967)

SmalltalkFirst pure object-oriented language (early 1980’s)Everything in the language is an object


Languages: Object-orientedC++

Introduced in the mid 1980’sBased on the C languageHybrid language: procedural & object-orientedExample:

// This C++ program finds the sum of 16 and 23,// then displays the result.

#include <iostream.h>

void main(void){ int sum; sum = 16 + 23; cout << "The sum of 16 and 23 is " << sum << endl;}


Languages: Object-orientedJava

Introduced in 1995 by Sun MicrosystemsObject-oriented language, but not as pure as Smalltalk

•In Java, primitive values (numbers, characters) are not objects -- they are values•In Smalltalk, everything is an object

During its research, was designed for use in appliancesReleased version designed for use on the Internet and as

a general-purpose programming languageProbably the most famous programming language of all

time•Lots of coverage in regular news, unlike other programming languages•Huge excitement about the language

programming and problem solving with java copyright 1999, james m. slack introduction what is a...

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