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*
 
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Oracle designates this
 
* particular file as subject to the "Classpath" exception as provided
 
* by Oracle in the LICENSE file that accompanied this code.
 
*
 
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 
* FITNESS FOR A PARTICULAR PURPOSE.
  
See the GNU General Public License
 
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* accompanied this code).
 
*
 
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* 2 along with this work; if not, write to the Free Software Foundation,
 
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*
 
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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
 
*
 
* @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);
}