According to the Java ``++Comparable.compareTo(T o)++`` documentation:


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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." 

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If this rule is violated, weird and unpredictable failures can occur.

For example, in Java 5 the ``++PriorityQueue.remove()++`` method relied on ``++compareTo()++``, but since Java 6 it has relied on ``++equals()++``.