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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 natural
* ordering, and the class's {@code compareTo} method is referred to as
* its natural comparison method.
*
* 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}.
*
* The natural ordering for a class {@code C} is said to be consistent
* with equals if and only if {@code e1.compareTo(e2) == 0} has
* the same boolean value as {@code e1.equals(e2)} for every
* {@code e1} and {@code e2} of class {@code C}. Note that {@code null}
* is not an instance of any class, and {@code e.compareTo(null)} should
* throw a {@code NullPointerException} even though {@code e.equals(null)}
* returns {@code 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 {@code equals}
* method.
*
* For example, if one adds two keys {@code a} and {@code b} such that
* {@code (!a.equals(b) && a.compareTo(b) == 0)} to a sorted
* set that does not use an explicit comparator, the second {@code add}
* operation returns false (and the size of the sorted set does not increase)
* because {@code a} and {@code b} are equivalent from the sorted set's
* perspective.
*
* Virtually all Java core classes that implement {@code Comparable}
* have natural orderings that are consistent with equals. One
* exception is {@link java.math.BigDecimal}, whose {@linkplain
* java.math.BigDecimal#compareTo natural ordering} equates {@code
* BigDecimal} objects with equal numerical values and different
* representations (such as 4.0 and 4.00). For {@link
* java.math.BigDecimal#equals BigDecimal.equals()} to return true,
* the representation and numerical value of the two {@code
* BigDecimal} objects must be the same.
*
* For the mathematically inclined, the relation that defines
* the natural ordering on a given class C is:
{@code
* {(x, y) such that x.compareTo(y) <= 0}.
* } The quotient for this total order is: {@code
* {(x, y) such that x.compareTo(y) == 0}.
* }
*
* It follows immediately from the contract for {@code compareTo} that the
* quotient is an equivalence relation on {@code C}, and that the
* natural ordering is a total order on {@code 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 {@link Object#equals(Object) equals(Object)} method:
* {(x, y) such that x.equals(y)}.
*
* In other words, when a class's natural ordering is consistent with
* equals, the equivalence classes defined by the equivalence relation
* of the {@code equals} method and the equivalence classes defined by
* the quotient of the {@code compareTo} method are the same.
*
*
This interface is a member of the
*
* Java Collections Framework.
*
* @param the type of objects that this object may be compared to
*
* @author Josh Bloch
* @see java.util.Comparator
* @since 1.2
*/
public interface Comparable {
/**
* 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 {@link Integer#signum
* signum}{@code (x.compareTo(y)) == -signum(y.compareTo(x))} for
* all {@code x} and {@code y}. (This implies that {@code
* x.compareTo(y)} must throw an exception if and only if {@code
* y.compareTo(x)} throws an exception.)
*
*
The implementor must also ensure that the relation is transitive:
* {@code (x.compareTo(y) > 0 && y.compareTo(z) > 0)} implies
* {@code x.compareTo(z) > 0}.
*
*
Finally, the implementor must ensure that {@code
* x.compareTo(y)==0} implies that {@code signum(x.compareTo(z))
* == signum(y.compareTo(z))}, for all {@code z}.
*
* @apiNote
* It is strongly recommended, but not strictly required that
* {@code (x.compareTo(y)==0) == (x.equals(y))}. Generally speaking, any
* class that implements the {@code Comparable} 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."
*
* @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);
}