1 /* Comparable.java -- Interface for comparaing objects to obtain an ordering
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42 * Interface for objects that can be ordering among other objects. The
43 * ordering can be <em>total</em>, such that two objects only compare equal
44 * if they are also equal by the equals method, or <em>partial</em> such
45 * that this is not necessarily true. For example, a case-sensitive
46 * dictionary order comparison of Strings is total, but if it is
47 * case-insensitive it is partial, because "abc" and "ABC" compare as
48 * equal even though "abc".equals("ABC") returns false. However, if you use
49 * a partial ordering, it is a good idea to document your class as
50 * "inconsistent with equals", because the behavior of your class in a
51 * SortedMap will be different than in a HashMap.
53 * <p>Lists, arrays, and sets of objects that implement this interface can
54 * be sorted automatically, without the need for an explicit
55 * {@link java.util.Comparator}. Note that <code>e1.compareTo(null)</code>
56 * should throw an Exception; as should comparison between incompatible
60 * @author Warren Levy <warrenl@cygnus.com>
61 * @see java.util.Comparator
62 * @see java.util.Collections#sort(java.util.List)
63 * @see java.util.Arrays#sort(Object[])
64 * @see java.util.SortedSet
65 * @see java.util.SortedMap
66 * @see java.util.TreeSet
67 * @see java.util.TreeMap
69 * @status updated to 1.4
71 public interface Comparable
74 * Compares this object with another, and returns a numerical result based
75 * on the comparison. If the result is negative, this object sorts less
76 * than the other; if 0, the two are equal, and if positive, this object
77 * sorts greater than the other. To translate this into boolean, simply
78 * perform <code>o1.compareTo(o2) <em><op></em> 0</code>, where op
79 * is one of <, <=, =, !=, >, or >=.
81 * <p>You must make sure that the comparison is mutual, ie.
82 * <code>sgn(x.compareTo(y)) == -sgn(y.compareTo(x))</code> (where sgn() is
83 * defined as -1, 0, or 1 based on the sign). This includes throwing an
84 * exception in either direction if the two are not comparable; hence,
85 * <code>compareTo(null)</code> should always throw an Exception.
87 * <p>You should also ensure transitivity, in two forms:
88 * <code>x.compareTo(y) > 0 && y.compareTo(z) > 0</code> implies
89 * <code>x.compareTo(z) > 0</code>; and <code>x.compareTo(y) == 0</code>
90 * implies <code>x.compareTo(z) == y.compareTo(z)</code>.
92 * @param o the object to be compared
93 * @return an integer describing the comparison
94 * @throws NullPointerException if o is null
95 * @throws ClassCastException if o cannot be compared
97 int compareTo(Object o
);