Page History

...

The general usage contract for {{compareTo()}} from Java SE 6 API \[[API 2006|AA. Java References#APIBibliography#API 06]\] states that:

The implementor must ensure sgn(x.compareTo(y)) == -sgn(y.compareTo(x)) for all x and y. (This implies that x.compareTo(y) must throw an exception iff y.compareTo(x) throws an exception.)

The implementor must also ensure that the relation is transitive: (x.compareTo(y) >0 && y.compareTo(z)>0) implies x.compareTo(z)>0.

Finally, the implementor must ensure that x.compareTo(y) ==0 implies that sgn(x.compareTo(z)) == sgn(y.compareTo(z)), for all z.

It is strongly recommended, but not strictly required that (x.compareTo(y) ==0) == (x.equals(y) ). Generally speaking, any class that implements the 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."

In the foregoing description, the notation sgn(expression) designates the mathematical signum function, which is defined to return either -1, 0, or 1 depending on whether the value of the expression is negative, zero or positive.

...

\[[API 2006|AA. Java References#APIBibliography#API 06]\] method [compareTo()|http://java.sun.com/javase/6/docs/api/java/lang/Comparable.html#compareTo(java.lang.Object)]
\[[JLS 2005|AA. Java References#JLSBibliography#JLS 05]\]

...

MET13-J. Ensure that hashCode() is overridden when equals() is overridden      16. Methods (MET)      MET15-J. Do not use deprecated or obsolete methods