SEI CERT Oracle Coding Standard for Java

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Comment: Edited by NavBot (vkp) v1.0

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Keys of ordered sets and maps should typically be immutable. If this is not possible, ensure that the {{equals()}} and {{compareTo()}} methods do not take into account the mutable state while comparing objects. Failure to do this, for example, can produce inconsistent orderings in collections. The documentation of {{java.util.Interface Set<E>}} and {{java.util.Interface Map<K,V>}} warn against this \[[API 2006|AA. Java References#APIBibliography#API 06]\]:

Note: great care must be exercised if mutable objects are used as map keys. The behavior of a map is not specified if the value of an object is changed in a manner that affects equals comparisons while the object is a key in the map. A special case of this prohibition is that it is not permissible for a map to contain itself as a key. While it is permissible for a map to contain itself as a value, extreme caution is advised: the equals and hashCode methods are no longer well defined on such a map.

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\[[API 2006|AA. Java References#APIBibliography#API 06]\] {{java.util.Interface Set<E>}} and {{java.util.Interface Map<K,V>}}

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