sonar规则适用未理解到位.docx
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sonar规则适用未理解到位
1.".equals（）"shouldnotbeusedtotestthevaluesof"Atomic"classes
AtomicInteger,and AtomicLong extend Number,butthey'redistinctfrom Integer and Long andshouldbehandleddifferently. AtomicInteger and AtomicLong aredesignedtosupportlock-free,thread-safeprogrammingonsinglevariables.Assuch,anAtomicInteger willonlyeverbe"equal"toitself.Instead,youshould .get（） thevalueandmakecomparisonsonit.
Thisappliestoalltheatomic,seeming-primitivewrapperclasses:
AtomicInteger, AtomicLong,and AtomicBoolean.
NoncompliantCodeExample
AtomicIntegeraInt1=newAtomicInteger（0）;
AtomicIntegeraInt2=newAtomicInteger（0）;
if（aInt1.equals（aInt2））{...}//Noncompliant
CompliantSolution
AtomicIntegeraInt1=newAtomicInteger（0）;
AtomicIntegeraInt2=newAtomicInteger（0）;
if（aInt1.get（）==aInt2.get（））{...}
".equals（）"不应该用来测试"Atomic"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.
NoncompliantCodeExample
doubled=1.1;
BigDecimalbd1=newBigDecimal（d）;//Noncompliant;seecommentabove
BigDecimalbd2=newBigDecimal（1.1）;//Noncompliant;sameresult
CompliantSolution
doubled=1.1;
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 compareTo againstaspecificvalueotherthan0couldresultinfalsenegatives.
NoncompliantCodeExample
if（myCpareTo（arg）==-1）{//Noncompliant
//...
}
CompliantSolution
if（myCpareTo（arg）<0）{
//...
}
"compareTo"不应该与具体的值做检查。
8."compareTo"shouldnotreturn"Integer.MIN_VALUE"
Itisthesign,ratherthanthemagnitudeofthevaluereturnedfrom compareTo thatmatters.Returning Integer.MIN_VALUE doesnotconveyahigherdegreeofinequality,anddoingsocancauseerrorsbecausethereturnvalueof compareTo issometimesinversed,withtheexpectationthatnegativevaluesbecomepositive.However,inversing Integer.MIN_VALUE yields Integer.MIN_VALUE ratherthan Integer.MAX_VALUE.
NoncompliantCodeExample
publicintcompareTo（MyClass）{
if（condition）{
returnInteger.MIN_VALUE;//Noncompliant
}
CompliantSolution
publicintcompareTo（MyClass）{
if（condition）{
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.
NoncompliantCodeExample
publicDatetrunc（Datedate）{
returnDateUtils.truncate（date,Calendar.SECOND）;//Noncompliant
}
CompliantSolution
publicDatetrunc（Datedate）{
Instantinstant=date.toInstant（）;
instant=instant.truncatedTo（ChronoUnit.SECONDS）;
returnDate.from（instant）;
}
"DateUtils.truncate"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.
NoncompliantCodeExample
inti=42;
doubled=Double.longBitsToDouble（i）;//Noncompliant
Double.longBitsToDouble（）方法不建议被使用
13."entrySet（）"shouldbeiteratedwhenboththekeyandvalueareneeded
Whenonlythekeysfromamapareneededinaloop,iteratingthe keySet makessense.Butwhenboththekeyandthevalueareneeded,it'smoreefficienttoiteratethe entrySet,whichwillgiveaccesstoboththekeyandvalue,instead.
NoncompliantCodeExample
publicvoiddoSomethingWithMap（Mapmap）{
for（Stringkey:
map.keySet（））{//Noncompliant
Objectvalue=map.get（key）;
//...
}
}
CompliantSolution
publicvoiddoSomethingWithMap（Mapmap）{
for（Map.Entryentry:
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 instanceof theparent,theparentisnotan intanceof thechild.Forinstance,assumethat RaspberryextendsFruit andaddssomefields（requiringanewimplementationof equals）:
Fruitfruit=newFruit（）;
Raspberryraspberry=newRaspberry（）;
if（raspberryinstanceofFruit）{...}//true
if（fruitinstanceofRaspberry）{...}//false
Ifsimilar instanceof checkswereusedintheclasses' equals methods,thesymmetryprinciplewouldbebroken:
raspberry.equals（fruit）;//false
fruit.equals（raspberry）;//true
Additionally,non final classesshouldn'tuseahardcodedclassnameinthe equals methodbecausedoingsobreaksthemethodforsubclasses.Instead,makethecomparisondynamic.
Further,comparingtoanunrelatedclasstypebreaksthecontractforthatunrelatedtype,becausewhile thisClass.equals（unrelatedClass） canreturntrue, unrelatedClass.equals（thisClass） willnot.
NoncompliantCodeExample
publicclassFruitextendsFood{
privateSeasonripe;
publicbooleanequals（Objectobj）{
if（obj==this）{
returntrue;
}
if（Fruit.class==obj.getClass（））{//Noncompliant;brokenforchildclasses
returnripe.equals（（（Fruit）obj）.getRipe（））;
}
if（objinstanceofFruit）{//Noncompliant;brokenforchildclasses
returnripe.equals（（（Fruit）obj）.getRipe（））;
}
elseif（objinstanceofSeason）{//Noncompliant;symmetrybrokenforSeasonclass
//...
}
//...
CompliantSolution
publicclassFruitextendsFood{
privateSeasonripe;
publicbooleanequals（Objectobj）{
if（obj==this）{
returntrue;
}
if（this.getClass（）==obj.getClass（））{
returnripe.equals（（（Fruit）obj）.getRipe（））;
}
returnfalse;
}
"equals"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（）.
NoncompliantCodeExample
publicclassFooimplementsComparable{
@Override
publicintcompareTo（Foofoo）{/*...*/}//Noncompliantastheequals（Objectobj）methodisnotoverridden
}
CompliantSolution
publicclassFooimplementsComparable{
@Override
publicintcompareTo（Foofoo）{/*...*/}//Compliant
@Override
publicbooleanequals（Objectobj）{/*...*/}
}
使用"compareTo（Tobj）"时"equals（Objectobj）也应该重写
17."equals（Objectobj）"shouldtestargumenttype
BecausetheequalsmethodtakesagenericObjectasaparameter,anytypeofobjectmaybepassedtoit.Themethodshouldnotassumeitwillonlybeusedtotestobjectsofitsclasstype.Itmustinsteadchecktheparameter'stype.
NoncompliantCodeExample
publicbooleanequals（Objectobj）{
MyClassmc=（MyClass）obj;//Noncompliant
//...
}
CompliantSolution
publicbooleanequals（Objectobj）{
if（obj==null）
returnfalse;
if（this.getClass（）!
=obj.getClass（））
returnfalse;
MyClassmc=（MyClass）obj;
//...
}
"equals（Objectobj）"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.
NoncompliantCodeExample
publicstaticvoidmain（String[]args）
{
StringargStr=args.toString（）;//Noncompliant
intargHash=args.hashCode（）;//Noncompliant
CompliantSolution
publicstaticvoidmain（String[]args）
{
StringargStr=Arrays.toString（args）;
intargHash=Arrays.hashCode（args）;
"hashCode"and"toString"不应该被数组实例调用。
27."instanceof"operatorsthatalwaysreturn"true"or"false"shouldberemoved
instanceofoperatorsthatalwaysreturntrueorfalseareeitheruselessortheresultofamisunderstandingwhichcouldleadtounexpectedbehaviorinproduction.
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