java – 实现比较方法的规则

1. The implementor must ensure that sgn(compare(x,y)) == -sgn(compare(y,x)) for all x and y. (This implies that compare(x,y) must throw an exception if and only if compare(y,x) throws an
   exception.)
2. The implementor must also ensure that the relation is transitive: ((compare(x,y)>0) && (compare(y,z)>0)) implies compare(x,z)>0.
3. Finally,the implementor must ensure that compare(x,y)==0 implies that sgn(compare(x,z))==sgn(compare(y,z)) for all z.
4. It is generally the case,but not strictly required that (compare(x,y)==0) == (x.equals(y)). Generally speaking,any comparator that violates this condition should clearly indicate this fact. The recommended language is “Note: this comparator imposes orderings that are inconsistent with equals.”