java.lang

Interface Comparable<T>

Known Subinterfaces:
Delayed, Name, RunnableScheduledFuture<V>, ScheduledFuture<V>
Known Implementing Classes:
BigDecimal, BigInteger, Boolean, Byte, ByteBuffer, Calendar, Character, CharBuffer, Charset, CollationKey, CompositeName, CompoundName, Date, Date, Double, DoubleBuffer, Enum<T,extends,Enum,T>, File, Float, FloatBuffer, GregorianCalendar, IntBuffer, Integer, Long, LongBuffer, MappedByteBuffer, ObjectStreamField, Short, ShortBuffer, String, Time, Timestamp, URI, UUID

public interface Comparable<T>

Interface for objects that can be ordering among other objects. The ordering can be total, such that two objects only compare equal if they are also equal by the equals method, or partial such that this is not necessarily true. For example, a case-sensitive dictionary order comparison of Strings is total, but if it is case-insensitive it is partial, because "abc" and "ABC" compare as equal even though "abc".equals("ABC") returns false. However, if you use a partial ordering, it is a good idea to document your class as "inconsistent with equals", because the behavior of your class in a SortedMap will be different than in a HashMap.

Lists, arrays, and sets of objects that implement this interface can be sorted automatically, without the need for an explicit Comparator. Note that e1.compareTo(null) should throw an Exception; as should comparison between incompatible classes.

Since:
1.2
See Also:
Comparator, java.util.Collections.sort(java.util.List), Arrays.sort(Object[]), SortedSet, SortedMap, TreeSet, TreeMap

Method Summary

int
compareTo(T o)
Compares this object with another, and returns a numerical result based on the comparison.

Method Details

compareTo

public int compareTo(T o)
Compares this object with another, and returns a numerical result based on the comparison. If the result is negative, this object sorts less than the other; if 0, the two are equal, and if positive, this object sorts greater than the other. To translate this into boolean, simply perform o1.compareTo(o2) <op> 0, where op is one of <, <=, =, !=, >, or >=.

You must make sure that the comparison is mutual, ie. sgn(x.compareTo(y)) == -sgn(y.compareTo(x)) (where sgn() is defined as -1, 0, or 1 based on the sign). This includes throwing an exception in either direction if the two are not comparable; hence, compareTo(null) should always throw an Exception.

You should also ensure transitivity, in two forms: x.compareTo(y) > 0 && y.compareTo(z) > 0 implies x.compareTo(z) > 0; and x.compareTo(y) == 0 implies x.compareTo(z) == y.compareTo(z).

Parameters:
o - the object to be compared
Returns:
an integer describing the comparison
Throws:
NullPointerException - if o is null
ClassCastException - if o cannot be compared

Comparable.java -- Interface for comparaing objects to obtain an ordering Copyright (C) 1998, 1999, 2001, 2002, 2004, 2005 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.