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Bad
Smells
Baldoino
Fonseca
baldoino@ic.ufal.br
Introduc7on
• To
learn
common
design
problems
so
you
can
recognize
them
in
your
own
code.
• The
most
common
design
problems
result
from
code
that
is:
– Duplicated
– Unclear
– Complicated
Duplicated
Code
You
have
the
same
code
structure
in
more
than
one
place
Duplicated
Code
Similarity
between
two
expressions
in
two
methods
of
the
same
class
CapitalStrategy
+advisedLine(loan
:
Loan)
:
double
+termLoan(loan
:
Loan)
:
double
return
loan.getUnusedPercentage()*
loan.getCommitment()*
dura7on(loan)*
riskFactFor(loan);
return
loan.getCommitment()*
dura7on(loan)*
riskFactFor(loan);
+dura7on(loan
:
Loan)
:
double
+riskFactFor(loan
:
Loan)
:
double
Similarity
=
75%
Duplicated
Code
Similarity
between
two
expressions
in
subclasses
CapitalStrategy
+capital(loan
:
Loan)
:
double
+dura7on(loan
:
Loan)
:
double
+riskFactFor(loan
:
Loan)
:
double
CapitalStrategyAdvisedLine
+capital(loan
:
Loan)
:
double
CapitalStrategyTermLoan
+capital(loan
:
Loan)
:
double
+dura7on(loan
:
Loan)
:
double
return
loan.getUnusedPercentage()*
loan.getCommitment()*
dura7on(loan)*
riskFactFor(loan);
return
loan.getCommitment()*
dura7on(loan)*
riskFactFor(loan);
Similarity
=
75%
Duplicated
Code
Similarity
between
codes
in
two
unrelated
classes
Person
name
areaCode
number
getTelephoneNumber
Company
cnpj
officeAreaCode
officeNumber
getTelephoneNumber
Similarity
=
66%
Duplicated
Code
public
class
Loan
{
…
public
Loan(float
no7onal,
float
outstanding,
int
ra7ng,
Date
expiry){
this.strategy
=
new
TermROC();
this.no7onal
=
no7onal;
this.outstanding
=
outstanding;
this.ra7ng
=
ra7ng;
this.expiry
=
expiry;
}
public
Loan(float
no7onal,
float
outstanding,
int
ra7ng,
Date
expiry,
Date
maturity){
this.strategy
=
new
RevolvingTermROC();
this.no7onal
=
no7onal;
this.outstanding
=
outstanding;
this.ra7ng
=
ra7ng;
this.expiry
=
expiry;
this.maturity
=
maturity;
}
public
Loan(CapitalStrategy
strategy,
float
outstanding,
int
ra7ng,
Date
expiry,
Date
maturity){
this.strategy
=
strategy;
this.no7onal
=
no7onal;
this.outstanding
=
outstanding;
this.ra7ng
=
ra7ng;
this.expiry
=
expiry;
this.maturity
=
maturity;
}
80%
67%
67%
Duplicated
Code
Similarity
among
the
condi7onal
logic
applied
throughout
the
system
to
deal
with
a
null
object
MouseEventHandler
+mouseDown(…)
:
boolean
+mouseMove(…)
:
boolean
MainMenuApplet
+mouseDown(…)
:
boolean
+mouseMove(…)
:
boolean
Naviga7onApplet
+mouseDown(…)
:
boolean
+mouseMove(…)
:
boolean
If
(mouseEventHandler
!=
null)
return
mouseEventHandler.mouseMove(…);
return
true;
If
(mouseEventHandler
!=
null)
return
mouseEventHandler.mouseMove(…);
return
true;
100%
Long
Parameter
List
To
pass
in
as
parameters
everything
needed
by
a
rou7ne
Long
Method
The
size
of
the
parameter
list
analyze(start
:
String,
end
:
String,
startTime
:
int,
endTime,
amount,
data:
Type)
:
void
5
args
Long
Method
When
an
object
invokes
a
method,
then
passes
the
result
as
a
parameter
for
a
method
Int
basePrice
=
_quan7ty
*
_itemPrice;
discountLevel
=
getDiscountLevel();
Double
finalPrice
=
discountPrice
(
basePrice,
discountLevel);
1
result
Long
Method
You
are
geEng
several
values
from
an
object
and
passing
these
values
as
parameters
in
a
method
call
Int
low
=
range.getLow();
Int
high
=
range.getHigh();
withinPlan
=
plan.withinRange(low,
high);
2
values
Long
Method
You
have
a
group
of
parameters
that
naturally
go
together
-‐
Data
Clumps
Customer
amountInvoiceIn(start:Date,
end:Date)
amountReceivedIn(start:Date,
end:Date)
amountOverdueIn(start:Date,
end:Date)
2
parameters
3
places
Long
Method
A
method
is
trying
to
do
too
much
Long
Method
You
have
many
temporary
variables
…
Vegeta7on
vegeta7on
=
new
Vegeta7on(
);
Slope
slope
=
new
Slope(
);
Rain
=
new
Rain(
);
Soil
=
new
Soil(
);
Occupa7on
occupa7on
=
new
Occupa7on(
);
Region
region
=
new
Region(
);
…
Analyze
apply(
)
:
Strategy
6
temps
Long
Method
The
amount
of
switch
statement
for
dispatching
and
handling
request
CatalogApp
If
(
ac7onName.equals(NEW_WORKSHOP){
//lots
of
code
to
create
a
new
workshop
}
else
if
(ac7onName.equals(ALL_WORKSHOPS)
{
//lots
of
code
to
display
informa7on
about
all
workshops
}…
many
more
“else
if”
statements
2
ifs
2
requests
Long
Method
The
amount
of
switch
statement
to
gather
data
from
numerous
classes
with
different
interfaces
Node
StringBuffer
results
=
new
StringBuffer();
NodeIterator
nodes
=
parser.elements();
while(nodes.hasMoreNodes()){
Node
node
=
nodes.nextNode();
if(node
instanceof
StringNode){
…add
contents
to
results
}else
if(node
instanceof
LinkTag){
…add
contents
to
results
}else
if(node
instanceof
Tag){
…add
contents
to
results
}else
if…
}
}
return
retults.toString();
LinkTag
Tag
StringNode
…
TextExtractor
+extractText(
)
:
String
4
ifs
4
gather
data
Long
Method
The
amount
of
versions
of
an
algorithm
and
condiIonal
logical
to
choose
which
version
to
use
at
runIme
capital(){
if(expiry
==
null
&&
maturity
!=
null)
return
commitment*dura7on()*riskFactor();
if(expiry
==
null
&&
maturity
==
null){
if(getUnusedPercentage()
!=
1.0)
return
commitment*getUnusedPercentage()*
dura7on()*riskFactor();
else
return
(outstandingRiskAmount()*dura7on()*riskFactor()
+
(unusedRiskAmount()*dura7on()*unusedRiskFactor());
}
return
0.0;
}
Loan
+capital(
)
:
double
4
ifs
3
strategy
Long
Method
You
have
a
single
bulky
method
that
accumulates
informaIon
to
a
local
variable
String
result
=
new
String();
result
+=
“<“
+
tagName
+
“
”
+
auributes
+
“>”;
Iterator
it
=
children.iterator();
while(it.hasNext()){
TagNode
node
=
(TagNode)it.next();
result
+=
node.toString();
}
If(!
tagValue.equals(“
”))
result+=
tagValue;
result+=
“<”
+
tagName
+
“>”;
return
result;
TagNode
toString(
)
:
String
9
lines
Large
Class
A
class
is
trying
to
do
too
much
Large
Class
Fields
and
Methods
Home
dvd:
DVD
cd:
CD
watchMovie(…)
:
void
tv:
TV
tuner:
Tuner
light:
Light
temperature:
Temperature
projector:
Projector
endMovie(…)
:
void
listenToCd(…)
:
void
endCd(…)
:
void
listenToRadio(…)
:
void
endRadio(…)
:
void
…
7
lines
6
lines
Large
Class
The
condiIonal
expressions
that
control
an
object’s
state
transiIons
are
complex.
If
(
state
!=
REQUESTED
&&
state
!=
UNIX_REQUESTED)
return;
willBeHandledBy(admin);
If
(
state
==
REQUESTED)
state
=
CLAIMED;
else
if
(state
==
UNIX_REQUESTED)
state
=
UNIX_CLAIMED;
SystemPermission
state:
String
REQUESTED
:
String
claimedBy(…)
:
void
CLAMED:
String
GRANTED:
String
DENIED:
String
UNIX_REQUESTED:
String
UNIX_CLAIMED:
String
grantedBy(…)
:
void
deniedBy(…)
:
void
4
Verifica7ons
Large
Class
Numerous
methods
on
a
class
combine
elements
of
an
implicit
language
List
nonWhiteProductsBelowNineDollars
=
productFinder.belowPriceAvoidingAColor(9.00f,
Color.white);
SystemPermission
byColor(…)
:
List
byPrice(…)
:
List
bySize(…)
:
List
belowPriceAvoidingAColor(…)
:
List
byColorAndBelowPrice(…)
:
List
byColorSizeAndBelowPrice(…)
:
List
Client
6
lines
Divergent
Change
On
class
is
commonly
changed
in
different
ways
for
different
reasons.
Home
watchMovie(…)
:
void
endMovie(…)
:
void
listenToCd(…)
:
void
endCd(…)
:
void
listenToRadio(…)
:
void
endRadio(…)
:
void
…
onProjector(…)
:
void
offProjector(…)
:
void
8
methods
8
concerns
Shotgun
Surgery
When
every
7me
you
make
a
kind
of
change,
you
have
to
make
a
lot
of
Liule
changes
to
a
lot
of
different
classes
Movie
Cd
DVD
Radio
Projector
Media
Feature
Envy
A
method
that
seems
more
interested
in
a
class
other
than
the
one
it
actually
is
in.
Media
descrip7on:
String
gender
:
String
mediaDescrip7on(…)
:
String
Contact
email:
String
prefix:
String
getEmail(…)
:
String
areacode:
String
number:
String
webpage:
String
getPrefix(…)
:
String
getAreaCode(…)
:
String
getNumber(…)
:
String
getWebpage(…)
:
String
return
descrip7on
+
gender
+
getEmail()
+
getPrefix()
+
getAreaCode()
+
getNumber()
+
getWebpage();
6
interests
2
auributes
Primi7ve
Obsession
It
occurs
when
the
designer
uses
primi7ve
data
types
to
represent
domain
ideas
Primi7ve
Obsession
You
have
an
array
in
which
certain
elements
mean
different
things
String[]
row
=
new
String[3];
row[0]
=
“Liverpool”;
row[1]
=
“15”;
2
different
auributes
Primi7ve
Obsession
The
primiIve
value
controls
logic
in
a
class
and
the
primiIve
value
isn’t
type-‐safe
SystemPermission
state:
String
REQUESTED
:
String
claimedBy(…)
:
void
CLAMED:
String
GRANTED:
String
DENIED:
String
UNIX_REQUESTED:
String
UNIX_CLAIMED:
String
grantedBy(…)
:
void
deniedBy(…)
:
void
public
final
sta7c
String
REQUESTED
=
“REQUESTED”;
If(state.equals(REQUESTED))
state
=
CLAIMED;
7
Primi7ve
Types
Primi7ve
Obsession
You
have
a
data
item
that
needs
addiIonal
data
or
behavior.
Order
customer
:
String
Primi7ve
Obsession
You
have
an
immutable
type
code
that
affects
the
behavior
of
a
class.
Order
ENGINEER
:
int
SALESMAN:
int
type:
int
Lazy
Class
A
class
that
is
not
doing
enough
to
pay
for
itself.
Employee
Salesman
Only
one
subclass
Specula7ve
Generality
I
think
we
need
the
ability
to
this
kind
of
thing
someday.
Specula7ve
Generality
You
have
abstract
classes
that
aren’t
doing
much
Employee
Salesman
Only
one
subclass
Specula7ve
Generality
Methods
with
unused
parameters
Customer
getContact(date:Date)
1
unused
parameter
Specula7ve
Generality
The
name
of
a
method
does
not
reveal
its
purpose.
Customer
ge7nvcdtlmt
Message
Chains
The
client
is
coupled
to
the
structure
of
the
navigaIon.
object.getE().getD().getC().getB().getA().getValue();
6
chains
Middle
Man
A
class
is
doing
too
much
simple
delegaIon.
Middle
Man
If
only
a
few
methods
aren’t
doing
much
int
getRa7ng(){
return
(moreThanFiveLateDeliveries())
?
2
:
1;
}
Boolean
moreThanFiveLateDeliveries(){
return
_numberOfLateDeliveries
>
5;
}
1
line
Indecent
Exposure
It
occurs
when
methods
or
classes
that
ought
not
be
visible
to
clients
are
publicity
visible
to
them.
Indecent
Exposure
Methods
or
classes
that
ought
not
to
be
visible
to
clients
are
publicly
visible
to
them
ARributeDescriptor
+AuributeDescriptor(…)
BooleanDescriptor
+BooleanDescriptor
(…)
DefaultDescriptor
+DefaultDescriptor
(…)
ReferenceDescriptor
+ReferenceDescriptor
(…)
Client
3
subclass
Data
Class
These
are
classes
that
have
fields,
ge~ng
and
se~ng
method
for
fields,
and
nothing
else.
In
early
stages
these
classes
are
dumb
data
holders
and
are
almost
certainly
being
manipulated
in
far
too
much
detail
by
other
classes.
Data
Class
Fields
Home
+
dvd:
DVD
+
cd:
CD
+
tv:
TV
+
tuner:
Tuner
+
light:
Light
+
temperature:
Temperature
+
projector:
Projector
7
fields
Refused
Bequest
Subclasses
get
to
inherit
the
methods
and
data
of
their
parents.
But
what
if
they
don’t
want
or
need
what
they
are
given?
They
are
given
all
these
great
gis
and
pick
just
a
few
to
play
with.
Comments
TIP:
When
you
feel
the
need
to
write
a
comment,
first
try
to
refactor
the
code
so
that
any
comment
becomes
superfluous.Mais conteúdos dessa disciplina
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