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Never violate any of the first three conditions when implementing the compareTo() method. Implementations should conform to the fourth condition whenever possible.
Noncompliant Code Example (
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Rock-
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Paper-
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Scissors)
This program implements the classic game of rock-paper-scissors, using the compareTo() operator to determine the winner of a game.
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However, this game violates the notion of transitivity , because Rock beats Scissors, Scissors beats Paper, but Rock does not beat Paper.
Compliant Solution (
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Rock-
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Paper-
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Scissors)
This compliant solution implements the same game , but does not use the Comparable interface.
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The Coverity Prevent Version 5.0 MUTABLE_COMPARISON checker can detect the instances where compareTo method is reading from a non-constant field. If the non-constant field is modified, the value of compareTo might change, which may break program invariants.
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