Copyright 1999 CERN - European Organization for Nuclear Research.
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Note: It is generally a good idea for comparators to implement java.io.Serializable, as they may be used as ordering methods in serializable data structures. In order for the data structure to serialize successfully, the comparator (if provided) must implement Serializable.
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.)
The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0.
Finally, the implementer must ensure that compare(x, y)==0 implies that sgn(compare(x, z))==sgn(compare(y, z)) for all z.
comp1.equals(comp2)implies that sgn(comp1.compare(o1, o2))==sgn(comp2.compare(o1, o2)) for every element o1 and o2.
Note that it is always safe not to override Object.equals(Object). However, overriding this method may, in some cases, improve performance by allowing programs to determine that two distinct Comparators impose the same order.
objthe reference object with which to compare.
trueonly if the specified object is also a comparator and it imposes the same ordering as this comparator.