HOW COMPUTERS HOW COMPUTERS MANIPULATE DATAMANIPULATE DATA

Chapter 1

Coming up: Analog vs. Digital

1-2

Hardware and SoftwareHardware and SoftwareHardware

◦the physical, tangible parts of a computer keyboard,

monitor, disks, wires, chips, etc.

Software◦programs and data

a program is a series of instructions

A computer requires both hardware and software; otherwise useless without the other

Digital InformationDigital InformationComputers store all information digitally:

◦ numbers◦ text◦ graphics and images◦ video◦ audio◦ program instructions

In some way, all information is digitized - broken down into pieces and represented as numbers

Coming up: Representing Text Digitally

Representing Text DigitallyRepresenting Text DigitallyFor example, every character is stored as a

number, including spaces, digits, and punctuation

Corresponding upper and lower case letters are separate characters

H i , H e a t h e r .

72 105 44 32 72 101 97 116 104 101 114 46

Coming up: Binary Numbers

Binary NumbersBinary NumbersOnce information is digitized, it is represented and

stored in memory using the binary number system

A single binary digit (0 or 1) is called a bit

Devices that store and move information are cheaper and more reliable if they have to represent only two states

A single bit can represent two possible states, like a light bulb that is either on (1) or off (0)

Permutations of bits are used to store values

Coming up: Bit Permutations

Bit PermutationsBit Permutations1 bit

01

2 bits

00011011

3 bits

000001010011100101110111

4 bits

00000001001000110100010101100111

10001001101010111100110111101111

Each additional bit doubles the number of possible permutations

Coming up: Bit Permutations

Bit PermutationsBit PermutationsEach permutation can represent a particular

itemThere are 2N permutations of N bitsTherefore, N bits are needed to represent 2N

unique items21 = 2 items

22 = 4 items

23 = 8 items

24 = 16 items

25 = 32 items

1 bit ?

2 bits ?

3 bits ?

4 bits ?

5 bits ?

How manyitems can be

represented by

Coming up: Java and Unicode

Java and UnicodeJava and UnicodeHow do we map from numbers to characters?

In Java we use the Unicode specification

which maps each character to a 16-bit number.

So, how many possible characters can we have? 216 = 65536

ASCII is an older set that was 8-bits and thus could represent only 28=256

Note: The creators of Unicode started with ASCII, so the 256 ASCII character codes are a subset of Unicode

Coming up: Java and Unicode

Java and UnicodeJava and UnicodeSee:

http://www.alanwood.net/demos/ansi.html

Unicode also includes some non-printable characters like null, tab, line feed, delete,…

Why 65,000 characters? We only have 26 letters!

Coming up: Binary – How does the computer see numbers?

Binary – How does the computer Binary – How does the computer see numbers?see numbers?

Computers represent information digitally, but only using a series of 1s and 0s.

Binary = Base 2

Decimal = Base 10

Hexadecimal = Base 16

Coming up: Decimal Numbers (normal)

Decimal Numbers Decimal Numbers (normal)(normal)In decimal (base 10) we

represent a number between 0-9 with one digit. To get any higher we use another position

23

Coming up: Binary Conversions

Binary ConversionsBinary Conversions

5037 = 103*5 + 102*0 + 101*3 + 100*7

Now, what about Binary, which is Base 2?

Available digits then are 1 and 0 only.

Binary 101 is what in decimal?

Coming up: Binary Conversions

JokeJokeThere are only 10 kinds of people

in this world. Those who know binary and those who don’t.

Coming up: Hexadecimal – base 16

Hexadecimal – base 16Hexadecimal – base 16Base sixteen means we need 16 digits.. 0-9

is 10 digits, how do I get more? A,B,C,D,E,F are valid “digits” in Hex. A=10, B=11, C=12, D=13, E=14, F=15

So, a hex number looks like:◦ 3A or FFF or A2C4B

What is 1A in decimal?◦ 161*1 + 160*10 = 26 decimal

Normally hexadecimal numbers are preceded by “0x” which means it is a hex number.

Coming up: What is 0x20 in decimal?

How to convert from decimal to How to convert from decimal to binarybinaryGiven a number (24) find the

largest place value that is lower than the number

26 = 6425 = 3224 = 1623 = 822 = 421 = 220 = 1

Coming up: Convert 9 into binary

Next divide the number by the place value to determine the digit for that position

24/16 = 1 Repeat process with remainder

(8 in this example)8/8 = 1So I need a 1 in the 16 position

and 8 position:= 11000

Convert 9 into binaryConvert 9 into binary

26 = 6425 = 3224 = 1623 = 822 = 421 = 220 = 1

Coming up: Convert 7 into binary?

8 is the largest placevalue that fits inside 9, so

9/8 = 1Remainder is 11 is the largest place value that

fits in 1, so1/1 = 1Remainder is 0

1001 = 9

Convert 35 to Convert 35 to hexadecimalhexadecimal

163=4096162=256161=16160=1

Coming up: Conclusions

16 is the largest placevalue that fits inside 35, so

35/16 = 2Remainder is 33/1 = 3Remainder is 0

0x23 = 35

ConclusionsConclusions

You should understand the math to do conversions to/from binary/decimal/hexadecimal

We’ll use this later in a project and lab. You may even see a question on it on the exam

End of presentation

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JavaJavaA programming language specifies

the words and symbols that we can use to write a program

A programming language employs a set of rules that dictate how the words and symbols can be put together to form valid program statements

It was introduced in 1995 and it's popularity has grown quickly since

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Java Program StructureJava Program StructureIn the Java programming language:

◦A program is made up of one or more classes

◦A class contains one or more methods◦A method contains program

statements

A Java application always contains a method called main

See HelloWorld.java

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Java Program StructureJava Program Structure

public class HelloWorld

{

}

// comments about the class

class header

class body

Comments can be placed almost anywhere

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Java Program StructureJava Program Structure

public class HelloWorld

{

}

// comments about the class

public static void main (String[] args)

{

}

// comments about the method

method headermethod body

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IdentifiersIdentifiersAn identifier can be made up of letters, digits,

the underscore character ( _ ), and the dollar sign

Identifiers cannot begin with a digit

Java is case sensitive - Total, total, and TOTAL are different identifiers

By convention, programmers use different case styles for different types of identifiers, such as

◦ title case for class names - Lincoln

◦ upper case for constants - MAXIMUM

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Program DevelopmentProgram DevelopmentThe mechanics of developing a program

include several activities◦ writing the program in a specific

programming language (such as Java)◦ translating the program into a form that

the computer can execute investigating and fixing various types of errors that can occur

Software tools can be used to help with all parts of this process

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Language LevelsLanguage LevelsThere are four programming

language levels:◦machine language (CPU specific)◦assembly language◦high-level language◦fourth-generation language

The other levels were created to make it easier for a human being to read and write programs

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Programming LanguagesProgramming LanguagesEach type of CPU executes only a

particular machine languageA program must be translated into

machine language before it can be executed

A compiler is a software tool which translates source code into a specific target language

Often, that target language is the machine language for a particular CPU type

The Java approach is somewhat different

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Java TranslationJava TranslationThe Java compiler translates Java source

code into a special representation called bytecode

Java bytecode is not the machine language for any traditional CPU

Another software tool, called an interpreter, translates bytecode into machine language and executes it

Therefore the Java compiler is not tied to any particular machine

Java is considered to be architecture-neutral

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Syntax and SemanticsSyntax and SemanticsThe syntax rules of a language

define how we can put together symbols, reserved words, and identifiers to make a valid program

The semantics of a program statement define what that statement means (its purpose or role in a program)

A program that is syntactically correct is not necessarily logically (semantically) correct

A program will always do what we tell it to do, not what we meant to tell it to do

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ErrorsErrorsA program can have three types of errorsThe compiler will find syntax errors and

other basic problems (compile-time errors)◦ If compile-time errors exist, an executable

version of the program is not createdA problem can occur during program

execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors)

A program may run, but produce incorrect results, perhaps using an incorrect formula (logical errors)

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Basic Program Basic Program DevelopmentDevelopment

errors

errors

Edit andsave program

Compile program

Execute program andevaluate results

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Problem SolvingProblem SolvingThe purpose of writing a program is to solve a

problem

Solving a problem consists of multiple activities:

◦ Understand the problem

◦ Design a solution

◦ Consider alternatives and

refine the solution

◦ Implement the solution

◦ Test the solution

These activities are not purely linear – they overlap and interact

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Problem SolvingProblem SolvingThe key to designing a solution is

breaking it down into manageable pieces

When writing software, we design separate pieces that are responsible for certain parts of the solution

An object-oriented approach lends itself to this kind of solution decomposition

We will dissect our solutions into pieces called objects and classes

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Object-Oriented Object-Oriented ProgrammingProgrammingJava is an object-oriented programming

languageAs the term implies, an object is a

fundamental entity in a Java programObjects can be used effectively to

represent real-world entitiesFor instance, an object might represent a

particular employee in a companyEach employee object handles the

processing and data management related to that employee

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ObjectsObjectsAn object has:

◦ state - descriptive characteristics

◦ behaviors - what it can do (or what can be done to it)

The state of a bank account includes its current balance

The behaviors associated with a bank account include the ability to make deposits and withdrawals

Note that the behavior of an object might change its state

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ClassesClassesAn object is defined by a class

A class is the blueprint of an object

The class uses methods to define the behaviors of the object

The class that contains the main method of a Java program represents the entire program

A class represents a concept, and an object represents the embodiment of that concept

Multiple objects can be created from the same class

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Objects and ClassesObjects and Classes

Bank Account

A class(the concept)

John’s Bank AccountBalance: $5,257

An object(the realization)

Bill’s Bank AccountBalance: $1,245,069

Mary’s Bank AccountBalance: $16,833

Multiple objectsfrom the same class