Chapter 3 focuses on - University of Victoriawebhome.cs.uvic.ca/~hausi/110/book/pdf/chap03.pdf · Java Software Solutions Lewis and Loftus Chapter 3 2 Copyright 1997 by John Lewis

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

1 C

opyright 1997 by John Lewis and W

illiam Loftus. A

ll rights reserved.

Program

Elem

ents -- Introduction

•W

e can now exam

ine the core elements of program

ming

•C

hapter 3 focuses on:

–data types

–variable declaration and use

–operators and expressions

–decisions and loops

–input and output

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

2 C


illiam Loftus. A

ll rights reserved.

Prim

itive Data T

ypes

•A

da

ta typ

e is defined by a set of values and the operators you can perform

on them

•E

ach value stored in mem

ory is associated with a

particular data type

•T

he Java language has several predefined types, called p

rimitive

da

ta typ

es

•T

he following reserved w

ords represent eight different prim

itive types:

–b

yte, sh

ort

, int

, lon

g, flo

at

, do

ub

le, b

oo

lea

n, ch

ar

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

3 C


illiam Loftus. A

ll rights reserved.

Integers

•T

here are four separate integer primitive data types

•T

hey differ by the amount of m

emory used to store them

Type

byteshortintlong

Storage

8 bits16 bits32 bits64 bits

Min V

alue

-128-32,768-2,147,483,648<

-9 x 10 18

Max V

alue

12732,7672,147,483,647>

9 x 10 18

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

4 C


illiam Loftus. A

ll rights reserved.

Floating P

oint

•T

here are two floating point types:

•T

he floa

t type stores 7 significant digits

•T

he do

ub

le

type stores 15 significant digits

Type

floatdouble

Storage

32 bits64 bits

Approxim

ateM

in Value

-3.4 x 10 38

-1.7 x 10 308

Approxim

ateM

ax Value

3.4 x 10 38

1.7 x 10 308

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

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illiam Loftus. A

ll rights reserved.

Characters

•A

cha

r value stores a single character from

the U

nico

de

cha

racte

r set

•A

cha

racte

r set is an ordered list of characters

•T

he Unicode character set uses sixteen bits per character,

allowing for 65,536 unique characters

•It is an international character set, containing sym

bols and characters from

many w

orld languages

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

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illiam Loftus. A

ll rights reserved.

Characters

•T

he AS

CII character set is still the basis for m

any other program

ming languages

•A

SC

II is a subset of Unicode, including:

uppercase letterslow

ercase letterspunctuationdigitsspecial sym

bolscontrol characters

A, B

, C, …

a, b, c, …period, sem

i-colon, …0, 1, 2, …&

, |, \, …carriage return, tab, ...

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

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illiam Loftus. A

ll rights reserved.

Boolean

•A

bo

ole

an

value represents a true or false condition

•T

hey can also be used to represent any two states, such

as a light bulb being on or off

•T

he reserved words tru

e

and false

are the only

valid values for a boolean type

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

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illiam Loftus. A

ll rights reserved.

Wrappers

•F

or each primitive data type there is a corresponding

wra

pp

er cla

ss. For exam

ple:

•W

rapper classes are useful in situations where you need

an object instead of a primitive type

•T

hey also contain some useful m

ethods

Prim

itive Type

int

do

ub

lech

ar

bo

ole

an

Wrapper C

lass

Inte

ge

rD

ou

ble

Ch

ara

cter

Bo

ole

an

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

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illiam Loftus. A

ll rights reserved.

Variables

•A

varia

ble is an identifier that represents a location in

mem

ory that holds a particular type of data

•V

ariables must be declared before they can be used

•T

he syntax of a variable declaration is:

d

ata

-type

varia

ble

-na

me

;

•F

or example:

int to

tal;

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

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illiam Loftus. A

ll rights reserved.

Variables

•M

ultiple variables can be declared on the same line:

int to

tal, co

un

t, sum

;

•V

ariables can be initialize

d (given an initial value) in the declaration:

int to

tal =

0, co

un

t = 2

0;

floa

t un

it_p

rice =

57

.25

;

•S

ee Pia

no

_K

eys.ja

va

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

11 C


illiam Loftus. A

ll rights reserved.

Assignm

ent Statem

ents

•A

n assignment statem

ent takes the following form

:

va

riab

le-n

am

e =

e

xpre

ssion

;

•T

he expression is evaluated and the result is stored in the variable, overw

riting the value currently stored in the variable

•S

ee Un

ited

_S

tate

s.java

•T

he expression can be a single value or a more

complicated calculation

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

12 C


illiam Loftus. A

ll rights reserved.

Constants

•A

constant is similar to a variable except that they keep

the same value throughout their existence

•T

hey are specified using the reserved word

fina

l in

the declaration

•F

or example:

fina

l do

ub

le P

I = 3

.14

15

9;

fina

l int S

TU

DE

NT

S =

25

;

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

13 C


illiam Loftus. A

ll rights reserved.

Constants

•W

hen appropriate, constants are better than variables because:

–they prevent inadvertent errors because their value cannot change

•T

hey are better than literal values because:

–they m

ake code more readable by giving m

eaning to a value

–they facilitate change because the value is only specified in one place

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

14 C


illiam Loftus. A

ll rights reserved.

Input and Output

•Java I/O

is based on in

pu

t strea

ms and o

utp

ut stre

am

s

•T

here are three predefined standard streams:

•T

he prin

t and p

rintln

m

ethods write to standard

output

Stream

Syste

m.in

Syste

m.o

ut

Syste

m.e

rr

Purpose

reading inputw

riting outputw

riting errors

Default D

evice

keyboardm

onitorm

onitor

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

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illiam Loftus. A

ll rights reserved.

Input and Output

•T

he Java AP

I allows you to create m

any kinds of streams

to perform various kinds of I/O

•T

o read character strings, we w

ill convert the

Syste

m.in

stream

to another kind of stream using:

Bu

ffere

dR

ea

de

r stdin

= n

ew

Bu

ffere

dR

ea

de

r

(ne

w In

pu

tStre

am

Re

ad

er (S

ystem

.in));

•T

his declaration creates a new stream

called std

in

•W

e will discuss object creation in m

ore detail later

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

16 C


illiam Loftus. A

ll rights reserved.

Escape S

equences

•S

ee Ech

o.ja

va

•A

n esca

pe

seq

ue

nce is a special sequence of characters

preceded by a backslash (\)

•T

hey indicate some special purpose, such as:

Escape S

equence

\t\n\"\'\\

Meaning

tabnew

linedouble quotesingle quotebackslash

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

17 C


illiam Loftus. A

ll rights reserved.

Buffers

•A

s you type, the characters are stored in an in

pu

t bu

ffer

•W

hen you press enter, the program begins processing the

data

•S

imilarly, output inform

ation is temporarily stored in an

ou

tpu

t bu

ffer

•T

he output buffer can be explicitly flu

she

d (sent to the screen) using the flu

sh

method

•S

ee Pyth

on

.java

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

18 C


illiam Loftus. A

ll rights reserved.

Num

eric Input

•C

onverting a string that holds an integer into the integer value can be done w

ith a method in the

Inte

ge

r w

rapper class:

valu

e =

Inte

ge

r.pa

rseIn

t (my_

string

);

•A

value can be read and converted in one line:

nu

m =

Inte

ge

r.pa

rseIn

t (stdin

.rea

dL

ine

());

•S

ee Ad

ditio

n.ja

va

and Ad

ditio

n2

.java

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

19 C


illiam Loftus. A

ll rights reserved.

Expressions

•A

n exp

ressio

n is a combination of operators and

operands

•T

he arithmetic operators include addition (

+), subtraction

(-), m

ultiplication (*), and division (/)

•O

perands can be literal values, variables, or other sources of data

•T

he programm

er determines w

hat is done with the result

of an expression (stored, printed, etc.)

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

20 C


illiam Loftus. A

ll rights reserved.

Division

•If the operands of the /

operator are both integers, the result is an integer (the fractional part is truncated)

•If one or m

ore operands to the /

operator are floating point values, the result is a floating point value

•T

he remainder operator (

%) returns the integer rem

ainder after dividing the first operand by the second

•T

he operands to the %

operator must be integers

•S

ee Divisio

n.ja

va

•T

he remainder result takes the sign of the num

erator

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

21 C


illiam Loftus. A

ll rights reserved.

Division

Expression

17

/ 51

7.0

/ 51

7 / 5

.0

9 / 1

29

.0 / 1

2.0

6 %

21

4 %

5-1

4 %

5

Result

33

.43

.400

.7504-4

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

22 C


illiam Loftus. A

ll rights reserved.

Operator P

recedence

•T

he order in which operands are evaluated in an

expression is determined by a w

ell-defined p

rece

de

nce

h

iera

rchy

•O

perators at the same level of precedence are evaluated

according to their associa

tivity (right to left or left to right)

•P

arentheses can be used to force precedence

•A

ppendix D contains a com

plete operator precedence chart for all Java operators

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

23 C


illiam Loftus. A

ll rights reserved.

Operator P

recedence

•M

ultiplication, division, and remainder have a higher

precedence than addition and subtraction

•B

oth groups associate left to right

Expression:

Order of evaluation:

Result:

5 +

12

/ 5 - 1

0 %

3

6

43

21

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

24 C


illiam Loftus. A

ll rights reserved.

Operator P

recedence

Expression

2 +

3 * 4

/ 2

3 * 1

3 +

2(3

* 13

) + 2

3 * (1

3 +

2)

4 * (1

1 - 6

) * (-8 +

10

)

(5 * (4

- 1)) / 2

Result

841

41

45

407

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

25 C


illiam Loftus. A

ll rights reserved.

The if S

tatement

•T

he Java if state

me

nt has the follow

ing syntax:

if (co

nd

ition

)

sta

tem

en

t;

•If the boolean condition is true, the statem

ent is executed; if it is false, the statem

ent is skipped

•T

his provides basic decision making capabilities

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

26 C


illiam Loftus. A

ll rights reserved.

The if S

tatement

statement

conditionfalse

true

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

27 C


illiam Loftus. A

ll rights reserved.

Boolean E

xpressions

•T

he condition of an if statem

ent must evaluate to a

true or false result

•Java has several equality and relational operators:

•S

ee Te

mp

era

ture

.java

Operator

==

!=<<=><=

Meaning

equal tonot equal to

less thanless than or equal to

greater thangreater than or equal to

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

28 C


illiam Loftus. A

ll rights reserved.

Block S

tatements

•S

everal statements can be grouped together into a

blo

ck sta

tem

en

t

•B

locks are delimited by braces

•A

block statement can be used w

herever a statement is

called for in the Java syntax

•S

ee Tem

pe

ratu

re2

.java

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

29 C


illiam Loftus. A

ll rights reserved.

The if-else S

tatement

•A

n e

lse

clause can be added to an if

statement to

make it an if-e

lse sta

tem

en

t:

if (co

nd

ition

)

sta

tem

en

t1;

else

sta

tem

en

t2;

•If the condition is true, statem

ent1 is executed; if the condition is false, statem

ent2 is executed

•S

ee Tem

pe

ratu

re3

.java

and R

igh

t_T

rian

gle

.java

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

30 C


illiam Loftus. A

ll rights reserved.

The if-else S

tatement

statement1

conditionfalse

true

statement2

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

31 C


illiam Loftus. A

ll rights reserved.

Nested if S

tatements

•T

he body of an if statem

ent or else

clause can be another if

statement

•T

hese are called n

este

d if sta

tem

en

ts

•S

ee Foo

tba

ll_C

ho

ice.ja

va

•N

ote: an else

clause is m

atched to the last unm

atched if (no m

atter what the indentation im

plies)

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

32 C


illiam Loftus. A

ll rights reserved.

The w

hile Statem

ent

•A

wh

ile sta

tem

en

t has the following syntax:

wh

ile (

con

ditio

n)

sta

tem

en

t;

•If the condition is true, the statem

ent is executed; then the condition is evaluated again

•T

he statement is executed over and over until the

condition becomes false

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

33 C


illiam Loftus. A

ll rights reserved.

The w

hile Statem

entstatement

conditionfalse

true

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

34 C


illiam Loftus. A

ll rights reserved.

The w

hile Statem

ent

•If the condition of a w

hile

statem

ent is false initially, the statem

ent is never executed

•T

herefore, we say that a

wh

ile

statement executes

zero or more tim

es

•S

ee Co

un

ter.ja

va, F

acto

rs.java

, and P

ow

ers_

of_

Tw

o.ja

va

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

35 C


illiam Loftus. A

ll rights reserved.

Infinite Loops

•T

he body of a wh

ile

loop must eventually m

ake the condition false

•If not, it is an in

finite

loo

p, which w

ill execute until the user interrupts the program

•T

his is a comm

on type of logical error -- always double

check that your loops will term

inate normally

•S

ee Fo

reve

r.java

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

36 C


illiam Loftus. A

ll rights reserved.

Program

Developm

ent

•T

he creation of software involves four basic activities:

–establishing the requirem

ents

–creating a design

–im

plementing the code

–testing the im

plementation

•T

he development process is m

uch more involved that

this, but these basic steps are a good starting point

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

37 C


illiam Loftus. A

ll rights reserved.

Requirem

ents

•R

equirements specify the tasks a program

must

accomplish (w

hat to do, not how to do it)

•T

hey often address the user interface

•A

n initial set of requirements are often provided, but

usually must be critiqued, m

odified, and expanded

•It is often difficult to establish detailed, unam

biguous, com

plete requirements

•C

areful attention to the requirements can save significant

time and m

oney in the overall project

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

38 C


illiam Loftus. A

ll rights reserved.

Design

•A

program follow

s an algo

rithm

, which is a step-by-step

process for solving a problem

•T

he design specifies the algorithms and data needed

•In object-oriented developm

ent, it establishes the classes, objects, and m

ethods that are required

•T

he details of a method m

ay be expressed in p

seu

do

cod

e, which is code-like, but does not necessarily

follow any specific syntax

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

39 C


illiam Loftus. A

ll rights reserved.

Implem

entation

•Im

plementation is the process of translating a design into

source code

•M

ost novice programm

ers think that writing code is the

heart of software developm

ent, but it actually should be the least creative

•A

lmost all im

portant decisions are made during

requirements analysis and design

•Im

plementation should focus on coding details,

including style guidelines and documentation

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

40 C


illiam Loftus. A

ll rights reserved.

Testing

•A

program should be executed m

ultiple times w

ith various input in an attem

pt to find errors

•D

eb

ug

gin

g is the process of discovering the cause of a problem

and fixing it

•P

rogramm

ers often erroneously think that there is "only one m

ore bug" to fix

•T

ests should focus on design details as well as overall

requirements

Java Softw

are Solutions Lew

is and Loftus

Chapter 3

41 C


illiam Loftus. A

ll rights reserved.

Program

Developm

ent

•S

ee Ave

rag

e.ja

va

•F

ollow the process of requirem

ents analysis, design, im

plementation, and testing

•T

here are always m

ultiple ways to design and im

plement

a program

•A

ny design has advantages and disadvantages; there are alw

ays trade-offs

•S

ee Ave

rag

e2

.java

Chapter 3 focuses on - University of Victoriawebhome.cs.uvic.ca/~hausi/110/book/pdf/chap03.pdf · Java Software Solutions Lewis and Loftus Chapter 3 2 Copyright 1997 by John Lewis

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