 Type Parameters:
T
 the type of objects that this object may be compared to
 All Known Subinterfaces:
ChronoLocalDate
,ChronoLocalDateTime<D>
,Chronology
,ChronoZonedDateTime<D>
,Delayed
,Name
,Path
,ProcessHandle
,RunnableScheduledFuture<V>
,ScheduledFuture<V>
 All Known Implementing Classes:
AbstractChronology
,AbstractRegionPainter.PaintContext.CacheMode
,AccessMode
,AclEntryFlag
,AclEntryPermission
,AclEntryType
,Authenticator.RequestorType
,BigDecimal
,BigInteger
,Boolean
,Byte
,ByteBuffer
,Calendar
,CatalogFeatures.Feature
,CertPathValidatorException.BasicReason
,Character
,Character.UnicodeScript
,CharBuffer
,Charset
,ChronoField
,ChronoUnit
,ClientInfoStatus
,CollationKey
,Collector.Characteristics
,Component.BaselineResizeBehavior
,CompositeName
,CompoundName
,CRLReason
,CryptoPrimitive
,Date
,Date
,DayOfWeek
,Desktop.Action
,Diagnostic.Kind
,Dialog.ModalExclusionType
,Dialog.ModalityType
,DirectMethodHandleDesc.Kind
,DocumentationTool.Location
,Double
,DoubleBuffer
,DrbgParameters.Capability
,DropMode
,Duration
,ElementKind
,Elements.Origin
,ElementType
,Enum
,File
,FileTime
,FileVisitOption
,FileVisitResult
,Float
,FloatBuffer
,FocusEvent.Cause
,FormatStyle
,Formatter.BigDecimalLayoutForm
,FormSubmitEvent.MethodType
,GraphicsDevice.WindowTranslucency
,GregorianCalendar
,GroupLayout.Alignment
,HijrahChronology
,HijrahDate
,HijrahEra
,HttpClient.Redirect
,HttpClient.Version
,Instant
,IntBuffer
,Integer
,IsoChronology
,IsoEra
,JapaneseChronology
,JapaneseDate
,JavaFileObject.Kind
,JDBCType
,JTable.PrintMode
,KeyRep.Type
,LayoutStyle.ComponentPlacement
,LdapName
,LinkOption
,LocalDate
,LocalDateTime
,Locale.Category
,Locale.FilteringMode
,Locale.IsoCountryCode
,LocalTime
,Long
,LongBuffer
,MappedByteBuffer
,MemoryType
,MinguoChronology
,MinguoDate
,MinguoEra
,Modifier
,ModuleDescriptor
,ModuleDescriptor.Exports
,ModuleDescriptor.Exports.Modifier
,ModuleDescriptor.Modifier
,ModuleDescriptor.Opens
,ModuleDescriptor.Opens.Modifier
,ModuleDescriptor.Provides
,ModuleDescriptor.Requires
,ModuleDescriptor.Requires.Modifier
,ModuleDescriptor.Version
,ModuleElement.DirectiveKind
,Month
,MonthDay
,MultipleGradientPaint.ColorSpaceType
,MultipleGradientPaint.CycleMethod
,NestingKind
,Normalizer.Form
,NumberFormat.Style
,NumericShaper.Range
,ObjectInputFilter.Status
,ObjectName
,ObjectStreamField
,OffsetDateTime
,OffsetTime
,PKIXReason
,PKIXRevocationChecker.Option
,PosixFilePermission
,ProcessBuilder.Redirect.Type
,Proxy.Type
,PseudoColumnUsage
,QuitStrategy
,Rdn
,ResolverStyle
,RetentionPolicy
,RoundingMode
,RowFilter.ComparisonType
,RowIdLifetime
,RowSorterEvent.Type
,Runtime.Version
,Short
,ShortBuffer
,SignStyle
,SortOrder
,SourceVersion
,SSLEngineResult.HandshakeStatus
,SSLEngineResult.Status
,StackWalker.Option
,StandardCopyOption
,StandardLocation
,StandardOpenOption
,StandardProtocolFamily
,String
,StringBuffer
,StringBuilder
,SwingWorker.StateValue
,System.Logger.Level
,Taskbar.Feature
,Taskbar.State
,TextStyle
,ThaiBuddhistChronology
,ThaiBuddhistDate
,ThaiBuddhistEra
,Thread.State
,Time
,Timestamp
,TimeUnit
,TrayIcon.MessageType
,TypeKind
,URI
,UserSessionEvent.Reason
,UUID
,VarHandle.AccessMode
,Window.Type
,XPathEvaluationResult.XPathResultType
,Year
,YearMonth
,ZonedDateTime
,ZoneOffset
,ZoneOffsetTransition
,ZoneOffsetTransitionRule.TimeDefinition
public interface Comparable<T>
compareTo
method is referred to as
its natural comparison method.
Lists (and arrays) of objects that implement this interface can be sorted
automatically by Collections.sort
(and
Arrays.sort
). Objects that implement this
interface can be used as keys in a sorted map or as
elements in a sorted set, without the need to
specify a comparator.
The natural ordering for a class C
is said to be consistent
with equals if and only if e1.compareTo(e2) == 0
has
the same boolean value as e1.equals(e2)
for every
e1
and e2
of class C
. Note that null
is not an instance of any class, and e.compareTo(null)
should
throw a NullPointerException
even though e.equals(null)
returns false
.
It is strongly recommended (though not required) that natural orderings be
consistent with equals. This is so because sorted sets (and sorted maps)
without explicit comparators behave "strangely" when they are used with
elements (or keys) whose natural ordering is inconsistent with equals. In
particular, such a sorted set (or sorted map) violates the general contract
for set (or map), which is defined in terms of the equals
method.
For example, if one adds two keys a
and b
such that
(!a.equals(b) && a.compareTo(b) == 0)
to a sorted
set that does not use an explicit comparator, the second add
operation returns false (and the size of the sorted set does not increase)
because a
and b
are equivalent from the sorted set's
perspective.
Virtually all Java core classes that implement Comparable
have natural
orderings that are consistent with equals. One exception is
java.math.BigDecimal
, whose natural ordering equates
BigDecimal
objects with equal values and different precisions
(such as 4.0 and 4.00).
For the mathematically inclined, the relation that defines the natural ordering on a given class C is:
{(x, y) such that x.compareTo(y) <= 0}.
The quotient for this total order is:
{(x, y) such that x.compareTo(y) == 0}.
It follows immediately from the contract for compareTo
that the
quotient is an equivalence relation on C
, and that the
natural ordering is a total order on C
. When we say that a
class's natural ordering is consistent with equals, we mean that the
quotient for the natural ordering is the equivalence relation defined by
the class's equals(Object)
method:{(x, y) such that x.equals(y)}.
This interface is a member of the Java Collections Framework.
 Since:
 1.2
 See Also:
Comparator

Method Details

compareTo
Compares this object with the specified object for order. Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.The implementor must ensure
sgn(x.compareTo(y)) == sgn(y.compareTo(x))
for allx
andy
. (This implies thatx.compareTo(y)
must throw an exception iffy.compareTo(x)
throws an exception.)The implementor must also ensure that the relation is transitive:
(x.compareTo(y) > 0 && y.compareTo(z) > 0)
impliesx.compareTo(z) > 0
.Finally, the implementor must ensure that
x.compareTo(y)==0
implies thatsgn(x.compareTo(z)) == sgn(y.compareTo(z))
, for allz
.It is strongly recommended, but not strictly required that
(x.compareTo(y)==0) == (x.equals(y))
. Generally speaking, any class that implements theComparable
interface and violates this condition should clearly indicate this fact. The recommended language is "Note: this class has a natural ordering that is inconsistent with equals."In the foregoing description, the notation
sgn(
expression)
designates the mathematical signum function, which is defined to return one of1
,0
, or1
according to whether the value of expression is negative, zero, or positive, respectively. Parameters:
o
 the object to be compared. Returns:
 a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.
 Throws:
NullPointerException
 if the specified object is nullClassCastException
 if the specified object's type prevents it from being compared to this object.
