java.lang.Comparable翻译

package java.lang;
import java.util.*;

/**
This interface imposes a total ordering on the objects of each class that implements it.  
#对所有实现Comparable接口的每一个类的全部对象进行强排序.

This ordering is referred to as the class's natural ordering, 
#这种排序被称为类的自然排序, 

and the class's {@code compareTo} method is referred to as its natural comparison method.

#类的方法compareTo()被称为它的自然比较方法.

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}).  
#实现了Comparable接口的集合(数组)可通过Collections.sort(Arrays.sort)自动排序.

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
{@code java.math.BigDecimal}, whose natural ordering equates
{@code BigDecimal} objects with equal values and different precisions
(such as 4.0 and 4.00).


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)}. 


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 {
 /**
 #为了排序 对象和指定的对象比较 .
 Compares this object with the specified object for order.  
 
 #返回一个负数, 零, 或一个正数 对应的是这个对象小于, 等于, 或大于指定的对象.
 Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.
 
 #实现者还必须确保: 
 #对于所有的x,y : sgn(x.compareTo(y)) == -sgn(y.compareTo(x)).
 #(这意味着: 当且仅当y.compareTo(x) 抛异常时, x.compareTo(y) 必然抛异常.)
 
The implementor must ensure : 
 {@code sgn(x.compareTo(y)) == -sgn(y.compareTo(x))} for all {@code x} and {@code y}.  
 (This implies that {@code x.compareTo(y)} must throw an exception iff {@code y.compareTo(x)} throws an exception.)
 
 #实现者还必须确保该关系是可传递的: x>y && y>z 必然 x>z
 
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}.
 
 #最后,实现者还必须确保: x.compareTo(y)==0 表示 sgn(x.compareTo(z)) == sgn(y.compareTo(z))
 
Finally, the implementor must ensure that {@code x.compareTo(y)==0} 
 implies that {@code sgn(x.compareTo(z)) == sgn(y.compareTo(z))}, for all {@code z}.
 
 #强烈建议, 但不严格要求, (x.compareTo(y)==0) == (x.equals(y))
 # 一般来说，任何实现Comparable接口并违反此条件的类应明确指出这一事实。 
 #推荐的语言是“注意：此类的自然排序与等式不一致”。
 
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."
 
 #在前面的描述中，符号sgn()表达式指定数学signum函数，该函数定义为返回{@code -1}之一，{@code 0}还是{@code 1}，具体取决于表达式的值分别为负，零或正。
 
In the foregoing description, the notation {@code sgn(}expression{@code )} designates the mathematical signum function, 
 which is defined to return one of {@code -1}, {@code 0}, or {@code 1} according to whether the value of expression is negative, zero, or positive, respectively.
 
 @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);
}

数学: 符号函数
x>0, sgnx= 1
x=0, sgnx= 0
x<0, sgnx=-1