Comparable (Java Platform SE 7 ) - Oracle Help Center

Interface Comparable. Type Parameters: T - the type of objects that this object may be compared to. Overview Package Class Use Tree Deprecated Index Help Java™ PlatformStandard Ed. 7 PrevClass NextClass Frames NoFrames AllClasses Summary:  Nested |  Field |  Constr |  Method Detail:  Field |  Constr |  Method TypeParameters:T-thetypeofobjectsthatthisobjectmaybecomparedto AllKnownSubinterfaces: Delayed,Name,Path,RunnableScheduledFuture,ScheduledFuture AllKnownImplementingClasses: AbstractRegionPainter.PaintContext.CacheMode,AccessMode,AclEntryFlag,AclEntryPermission,AclEntryType,AddressingFeature.Responses,Authenticator.RequestorType,BigDecimal,BigInteger,Boolean,Byte,ByteBuffer,Calendar,CertPathValidatorException.BasicReason,Character,Character.UnicodeScript,CharBuffer,Charset,ClientInfoStatus,CollationKey,Component.BaselineResizeBehavior,CompositeName,CompoundName,CRLReason,CryptoPrimitive,Date,Date,Desktop.Action,Diagnostic.Kind,Dialog.ModalExclusionType,Dialog.ModalityType,Double,DoubleBuffer,DropMode,ElementKind,ElementType,Enum,File,FileTime,FileVisitOption,FileVisitResult,Float,FloatBuffer,Formatter.BigDecimalLayoutForm,FormSubmitEvent.MethodType,GraphicsDevice.WindowTranslucency,GregorianCalendar,GroupLayout.Alignment,IntBuffer,Integer,JavaFileObject.Kind,JTable.PrintMode,KeyRep.Type,LayoutStyle.ComponentPlacement,LdapName,LinkOption,Locale.Category,Long,LongBuffer,MappedByteBuffer,MemoryType,MessageContext.Scope,Modifier,MultipleGradientPaint.ColorSpaceType,MultipleGradientPaint.CycleMethod,NestingKind,Normalizer.Form,NumericShaper.Range,ObjectName,ObjectStreamField,PKIXReason,PosixFilePermission,ProcessBuilder.Redirect.Type,Proxy.Type,PseudoColumnUsage,Rdn,Resource.AuthenticationType,RetentionPolicy,RoundingMode,RowFilter.ComparisonType,RowIdLifetime,RowSorterEvent.Type,Service.Mode,Short,ShortBuffer,SOAPBinding.ParameterStyle,SOAPBinding.Style,SOAPBinding.Use,SortOrder,SourceVersion,SSLEngineResult.HandshakeStatus,SSLEngineResult.Status,StandardCopyOption,StandardLocation,StandardOpenOption,StandardProtocolFamily,String,SwingWorker.StateValue,Thread.State,Time,Timestamp,TimeUnit,TrayIcon.MessageType,TypeKind,URI,UUID,WebParam.Mode,Window.Type,XmlAccessOrder,XmlAccessType,XmlNsForm publicinterfaceComparable Thisinterfaceimposesatotalorderingontheobjectsofeachclassthat implementsit.Thisorderingisreferredtoastheclass'snatural ordering,andtheclass'scompareTomethodisreferredtoas itsnaturalcomparisonmethod. Lists(andarrays)ofobjectsthatimplementthisinterfacecanbesorted automaticallybyCollections.sort(and Arrays.sort).Objectsthatimplementthis interfacecanbeusedaskeysinasortedmaporas elementsinasortedset,withouttheneedto specifyacomparator. ThenaturalorderingforaclassCissaidtobeconsistent withequalsifandonlyife1.compareTo(e2)==0has thesamebooleanvaluease1.equals(e2)forevery e1ande2ofclassC.Notethatnull isnotaninstanceofanyclass,ande.compareTo(null)should throwaNullPointerExceptioneventhoughe.equals(null) returnsfalse. Itisstronglyrecommended(thoughnotrequired)thatnaturalorderingsbe consistentwithequals.Thisissobecausesortedsets(andsortedmaps) withoutexplicitcomparatorsbehave"strangely"whentheyareusedwith elements(orkeys)whosenaturalorderingisinconsistentwithequals.In particular,suchasortedset(orsortedmap)violatesthegeneralcontract forset(ormap),whichisdefinedintermsoftheequals method. Forexample,ifoneaddstwokeysaandbsuchthat (!a.equals(b)&&a.compareTo(b)==0)toasorted setthatdoesnotuseanexplicitcomparator,thesecondadd operationreturnsfalse(andthesizeofthesortedsetdoesnotincrease) becauseaandbareequivalentfromthesortedset's perspective. VirtuallyallJavacoreclassesthatimplementComparablehavenatural orderingsthatareconsistentwithequals.Oneexceptionis java.math.BigDecimal,whosenaturalorderingequates BigDecimalobjectswithequalvaluesanddifferentprecisions (suchas4.0and4.00). Forthemathematicallyinclined,therelationthatdefines thenaturalorderingonagivenclassCis: {(x,y)suchthatx.compareTo(y)<=0}. Thequotientforthistotalorderis: {(x,y)suchthatx.compareTo(y)==0}. ItfollowsimmediatelyfromthecontractforcompareTothatthe quotientisanequivalencerelationonC,andthatthe naturalorderingisatotalorderonC.Whenwesaythata class'snaturalorderingisconsistentwithequals,wemeanthatthe quotientforthenaturalorderingistheequivalencerelationdefinedby theclass'sequals(Object)method: {(x,y)suchthatx.equals(y)}. Thisinterfaceisamemberofthe JavaCollectionsFramework. Since: 1.2 SeeAlso:Comparator MethodSummary Methods  ModifierandType MethodandDescription int compareTo(T o) Comparesthisobjectwiththespecifiedobjectfororder. MethodDetail compareTo int compareTo(T o) Comparesthisobjectwiththespecifiedobjectfororder.Returnsa negativeinteger,zero,orapositiveintegerasthisobjectisless than,equalto,orgreaterthanthespecifiedobject. Theimplementormustensuresgn(x.compareTo(y))== -sgn(y.compareTo(x))forallxandy.(This impliesthatx.compareTo(y)mustthrowanexceptioniff y.compareTo(x)throwsanexception.) Theimplementormustalsoensurethattherelationistransitive: (x.compareTo(y)>0&&y.compareTo(z)>0)implies x.compareTo(z)>0. Finally,theimplementormustensurethatx.compareTo(y)==0 impliesthatsgn(x.compareTo(z))==sgn(y.compareTo(z)),for allz. Itisstronglyrecommended,butnotstrictlyrequiredthat (x.compareTo(y)==0)==(x.equals(y)).Generallyspeaking,any classthatimplementstheComparableinterfaceandviolates thisconditionshouldclearlyindicatethisfact.Therecommended languageis"Note:thisclasshasanaturalorderingthatis inconsistentwithequals." Intheforegoingdescription,thenotation sgn(expression)designatesthemathematical signumfunction,whichisdefinedtoreturnoneof-1, 0,or1accordingtowhetherthevalueof expressionisnegative,zeroorpositive. Parameters:o-theobjecttobecompared. Returns:anegativeinteger,zero,orapositiveintegerasthisobject islessthan,equalto,orgreaterthanthespecifiedobject. Throws: NullPointerException-ifthespecifiedobjectisnull ClassCastException-ifthespecifiedobject'stypepreventsit frombeingcomparedtothisobject. Overview Package Class Use Tree Deprecated Index Help Java™ PlatformStandard Ed. 7 PrevClass NextClass Frames NoFrames AllClasses Summary:  Nested |  Field |  Constr |  Method Detail:  Field |  Constr |  Method SubmitabugorfeatureForfurtherAPIreferenceanddeveloperdocumentation,seeJavaSEDocumentation.Thatdocumentationcontainsmoredetailed,developer-targeteddescriptions,withconceptualoverviews,definitionsofterms,workarounds,andworkingcodeexamples.Copyright©1993,2020,Oracleand/oritsaffiliates.Allrightsreserved.Useissubjecttolicenseterms.Alsoseethedocumentationredistributionpolicy.