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package java.lang;







import java.util.*;














/**







 * This interface imposes a total ordering on the objects of each class that







 * implements it.  This ordering is referred to as the class's <i>natural







 * ordering</i>, and the class's <tt>compareTo</tt> method is referred to as







 * its <i>natural comparison method</i>.<p>







 *







 * Lists (and arrays) of objects that implement this interface can be sorted







 * automatically by {@link Collections#sort(List) Collections.sort} (and







 * {@link Arrays#sort(Object[]) Arrays.sort}).  Objects that implement this







 * interface can be used as keys in a {@linkplain SortedMap sorted map} or as







 * elements in a {@linkplain SortedSet sorted set}, without the need to







 * specify a {@linkplain Comparator comparator}.<p>







 *







 * The natural ordering for a class <tt>C</tt> is said to be <i>consistent







 * with equals</i> if and only if <tt>e1.compareTo(e2) == 0</tt> has







 * the same boolean value as <tt>e1.equals(e2)</tt> for every







 * <tt>e1</tt> and <tt>e2</tt> of class <tt>C</tt>.  Note that <tt>null</tt>







 * is not an instance of any class, and <tt>e.compareTo(null)</tt> should







 * throw a <tt>NullPointerException</tt> even though <tt>e.equals(null)</tt>







 * returns <tt>false</tt>.<p>







 *







 * 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 <tt>equals</tt>







 * method.<p>







 *







 * For example, if one adds two keys <tt>a</tt> and <tt>b</tt> such that







 * {@code (!a.equals(b) && a.compareTo(b) == 0)} to a sorted







 * set that does not use an explicit comparator, the second <tt>add</tt>







 * operation returns false (and the size of the sorted set does not increase)







 * because <tt>a</tt> and <tt>b</tt> are equivalent from the sorted set's







 * perspective.<p>







 *







 * Virtually all Java core classes that implement <tt>Comparable</tt> have natural







 * orderings that are consistent with equals.  One exception is







 * <tt>java.math.BigDecimal</tt>, whose natural ordering equates







 * <tt>BigDecimal</tt> objects with equal values and different precisions







 * (such as 4.0 and 4.00).<p>







 *







 * For the mathematically inclined, the <i>relation</i> that defines







 * the natural ordering on a given class C is:<pre>







 *       {(x, y) such that x.compareTo(y) &lt;= 0}.







 * </pre> The <i>quotient</i> for this total order is: <pre>







 *       {(x, y) such that x.compareTo(y) == 0}.







 * </pre>







 *







 * It follows immediately from the contract for <tt>compareTo</tt> that the







 * quotient is an <i>equivalence relation</i> on <tt>C</tt>, and that the







 * natural ordering is a <i>total order</i> on <tt>C</tt>.  When we say that a







 * class's natural ordering is <i>consistent with equals</i>, we mean that the







 * quotient for the natural ordering is the equivalence relation defined by







 * the class's {@link Object#equals(Object) equals(Object)} method:<pre>







 *     {(x, y) such that x.equals(y)}. </pre><p>







 *







 * This interface is a member of the







 * <a href="{@docRoot}/../technotes/guides/collections/index.html">







 * Java Collections Framework</a>.







 *







 * @param <T> the type of objects that this object may be compared to







 *







 * @author  Josh Bloch







 * @see java.util.Comparator







 * @since 1.2







 */







public interface Comparable<T> {







    /**







     * 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.







     *







     * <p>The implementor must ensure <tt>sgn(x.compareTo(y)) ==







     * -sgn(y.compareTo(x))</tt> for all <tt>x</tt> and <tt>y</tt>.  (This







     * implies that <tt>x.compareTo(y)</tt> must throw an exception iff







     * <tt>y.compareTo(x)</tt> throws an exception.)







     *







     * <p>The implementor must also ensure that the relation is transitive:







     * <tt>(x.compareTo(y)&gt;0 &amp;&amp; y.compareTo(z)&gt;0)</tt> implies







     * <tt>x.compareTo(z)&gt;0</tt>.







     *







     * <p>Finally, the implementor must ensure that <tt>x.compareTo(y)==0</tt>







     * implies that <tt>sgn(x.compareTo(z)) == sgn(y.compareTo(z))</tt>, for







     * all <tt>z</tt>.







     *







     * <p>It is strongly recommended, but <i>not</i> strictly required that







     * <tt>(x.compareTo(y)==0) == (x.equals(y))</tt>.  Generally speaking, any







     * class that implements the <tt>Comparable</tt> 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."







     *







     * <p>In the foregoing description, the notation







     * <tt>sgn(</tt><i>expression</i><tt>)</tt> designates the mathematical







     * <i>signum</i> function, which is defined to return one of <tt>-1</tt>,







     * <tt>0</tt>, or <tt>1</tt> according to whether the value of







     * <i>expression</i> is negative, zero or positive.







     *







     * @param   o the object to be compared.







     * @return  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 null







     * @throws ClassCastException if the specified object's type prevents it







     *         from being compared to this object.







     */







    public int compareTo(T o);







}






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