sonar规则适用未理解到位Word格式.docx
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AtomicBoolean.
NoncompliantCodeExample
AtomicIntegeraInt1=newAtomicInteger（0）;
AtomicIntegeraInt2=newAtomicInteger（0）;
if（aInt1.equals（aInt2））{...}//Noncompliant
CompliantSolution
if（aInt1.get（）==aInt2.get（））{...}
"
不应该用来测试"
类型的等值比较。
3."
BigDecimal（double）"
shouldnotbeused
Becauseoffloatingpointimprecision,you'
reunlikelytogetthevalueyouexpectfromthe
BigDecimal（double）
constructor.
From
theJavaDocs:
Theresultsofthisconstructorcanbesomewhatunpredictable.OnemightassumethatwritingnewBigDecimal（0.1）inJavacreatesaBigDecimalwhichisexactlyequalto0.1（anunscaledvalueof1,withascaleof1）,butitisactuallyequalto0.1000000000000000055511151231257827021181583404541015625.Thisisbecause0.1cannotberepresentedexactlyasadouble（or,forthatmatter,asabinaryfractionofanyfinitelength）.Thus,thevaluethatisbeingpassedintotheconstructorisnotexactlyequalto0.1,appearancesnotwithstanding.
Instead,youshoulduse
BigDecimal.valueOf,whichusesastringunderthecoverstoeliminatefloatingpointroundingerrors.
doubled=1.1;
BigDecimalbd1=newBigDecimal（d）;
//Noncompliant;
seecommentabove
BigDecimalbd2=newBigDecimal（1.1）;
sameresult
BigDecimalbd1=BigDecimal.valueOf（d）;
BigDecimalbd2=BigDecimal.valueOf（1.1）;
See
CERT,NUM10-J
-DonotconstructBigDecimalobjectsfromfloating-pointliterals
数值正确使用
7."
compareTo"
resultsshouldnotbecheckedforspecificvalues
Whilemost
compareTo
methodsreturn-1,0,or1,somedonot,andtestingtheresultofa
againstaspecificvalueotherthan0couldresultinfalsenegatives.
if（myCpareTo（arg）==-1）{//Noncompliant
//...
}
if（myCpareTo（arg）<
0）{
不应该与具体的值做检查。
8."
shouldnotreturn"
Integer.MIN_VALUE"
Itisthesign,ratherthanthemagnitudeofthevaluereturnedfrom
thatmatters.Returning
Integer.MIN_VALUE
doesnotconveyahigherdegreeofinequality,anddoingsocancauseerrorsbecausethereturnvalueof
issometimesinversed,withtheexpectationthatnegativevaluesbecomepositive.However,inversing
yields
ratherthan
Integer.MAX_VALUE.
publicintcompareTo（MyClass）{
if（condition）{
returnInteger.MIN_VALUE;
//Noncompliant
}
return-1;
状态值不应该用数值类型的边界值。
10."
DateUtils.truncate"
fromApacheCommonsLanglibraryshouldnotbeused
Theuseofthe
Instant
classintroducedinJava8totruncateadatecanbesignificantlyfasterthanthe
DateUtils
classfromCommonsLang.
publicDatetrunc（Datedate）{
returnDateUtils.truncate（date,Calendar.SECOND）;
//Noncompliant
Instantinstant=date.toInstant（）;
instant=instant.truncatedTo（ChronoUnit.SECONDS）;
returnDate.from（instant）;
正确使用,《不建议使用》
从效率上考虑的。
12."
Double.longBitsToDouble"
shouldnotbeusedfor"
int"
Double.longBitsToDouble
expectsa64-bit,
long
argument.Passitasmallervalue,suchasan
int
andthemathematicalconversionintoa
double
simplywon'
tworkasanticipatedbecausethelayoutofthebitswillbeinterpretedincorrectly,asifachildweretryingtouseanadult'
sgloves.
inti=42;
doubled=Double.longBitsToDouble（i）;
Double.longBitsToDouble（）方法不建议被使用
13."
entrySet（）"
shouldbeiteratedwhenboththekeyandvalueareneeded
Whenonlythekeysfromamapareneededinaloop,iteratingthe
keySet
makessense.Butwhenboththekeyandthevalueareneeded,it'
smoreefficienttoiteratethe
entrySet,whichwillgiveaccesstoboththekeyandvalue,instead.
publicvoiddoSomethingWithMap（Map<
String,Object>
map）{
for（Stringkey:
map.keySet（））{//Noncompliant
Objectvalue=map.get（key）;
for（Map.Entry<
entry:
map.entrySet（））{
Stringkey=entry.getKey（）;
Objectvalue=entry.getValue（）;
“entryset（）”应该是迭代时，键和值是必要的
keySet是键的集合，Set里面的类型即key的类型
entrySet是键-值对的集合，Set里面的类型是Map.Entry
14."
equals"
methodsshouldbesymmetricandworkforsubclasses
Akeyfacetofthe
equals
contractisthatif
a.equals（b）
then
b.equals（a）,i.e.thattherelationshipissymmetric.
Using
instanceof
breaksthecontractwhentherearesubclasses,becausewhilethechildisan
theparent,theparentisnotan
intanceof
thechild.Forinstance,assumethat
RaspberryextendsFruit
andaddssomefields（requiringanewimplementationof
equals）:
Fruitfruit=newFruit（）;
Raspberryraspberry=newRaspberry（）;
if（raspberryinstanceofFruit）{...}//true
if（fruitinstanceofRaspberry）{...}//false
Ifsimilar
checkswereusedintheclasses'
methods,thesymmetryprinciplewouldbebroken:
raspberry.equals（fruit）;
//false
fruit.equals（raspberry）;
//true
Additionally,non
final
classesshouldn'
tuseahardcodedclassnameinthe
methodbecausedoingsobreaksthemethodforsubclasses.Instead,makethecomparisondynamic.
Further,comparingtoanunrelatedclasstypebreaksthecontractforthatunrelatedtype,becausewhile
thisClass.equals（unrelatedClass）
canreturntrue,
unrelatedClass.equals（thisClass）
willnot.
publicclassFruitextendsFood{
privateSeasonripe;
publicbooleanequals（Objectobj）{
if（obj==this）{
returntrue;
}
if（Fruit.class==obj.getClass（））{//Noncompliant;
brokenforchildclasses
returnripe.equals（（（Fruit）obj）.getRipe（））;
if（objinstanceofFruit）{//Noncompliant;
elseif（objinstanceofSeason）{//Noncompliant;
symmetrybrokenforSeasonclass
//...
if（this.getClass（）==obj.getClass（））{
returnfalse;
子类也需要重写，equals一个重要属性是,如果a.equals（b）然后b.equals（A）,即是对称的关系。
建议使用此规则。
16."
equals（Objectobj）"
shouldbeoverriddenalongwiththe"
compareTo（Tobj）"
method
AccordingtotheJava
CpareTo（To）
documentation:
Itisstronglyrecommended,butnotstrictlyrequiredthat
（pareTo（y）==0）==（x.equals（y））.Generallyspeaking,anyclassthatimplementstheComparableinterfaceandviolatesthisconditionshouldclearlyindicatethisfact.Therecommendedlanguageis"
Note:
thisclasshasanaturalorderingthatisinconsistentwithequals."
Ifthisruleisviolated,weirdandunpredictablefailurescanoccur.Forexample,inJava5the
PriorityQueue.remove（）
methodreliedon
compareTo（）,butsinceJava6itrelieson
equals（）.
publicclassFooimplementsComparable<
Foo>
{
@Override
publicintcompareTo（Foofoo）{/*...*/}//Noncompliantastheequals（Objectobj）methodisnotoverridden
publicintcompareTo（Foofoo）{/*...*/}//Compliant
publicbooleanequals（Objectobj）{/*...*/}
使用"
时"
equals（Objectobj）也应该重写
17."
shouldtestargumenttype
BecausetheequalsmethodtakesagenericObjectasaparameter,anytypeofobjectmaybepassedtoit.Themethodshouldnotassumeitwillonlybeusedtotestobjectsofitsclasstype.Itmustinsteadchecktheparameter'
stype.
publicbooleanequals（Objectobj）{
MyClassmc=（MyClass）obj;
if（obj==null）
if（this.getClass（）!
=obj.getClass（））
应该是检验参数类型是否为Object。
23."
hashCode"
and"
toString"
shouldnotbecalledonarrayinstances
WhilehashCodeandtoStringareavailableonarrays,theyarelargelyuseless.hashCodereturnsthearray'
s"
identityhashcode"
andtoStringreturnsnearlythesamevalue.Neithermethod'
soutputactuallyreflectsthearray'
scontents.Instead,youshouldpassthearraytotherelevantstaticArraysmethod.
publicstaticvoidmain（String[]args）
{
StringargStr=args.toString（）;
intargHash=args.hashCode（）;
StringargStr=Arrays.toString（args）;
intargHash=Arrays.hashCode（args）;
不应该被数组实例调用。
27."
instanceof"
operatorsthatalwaysreturn"
true"
or"
false"
shouldberemoved
instanceofoperatorsthatalwaysreturntrueorfalseareeitheruselessortheresultofamisunderstandingwhichcouldleadtounexpectedbehaviorinproduction.
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