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"An inner class is a nested class that is not explicitly or implicitly declared {{static}}." \[[JLS 2005|AA. Bibliography#JLS 05]\]. Serialization of inner classes (including local and anonymous classes) is error prone. According to the Serialization Specification \[[Sun 2006|AA. Bibliography#Sun 06]\]:

• Because inner classes declared in non-static contexts contain implicit non-transient references to enclosing class instances, serializing such an inner class instance results in serialization of its associated outer class instance.

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• Because inner classes cannot declare static members other than compile-time constant fields, they cannot use the serialPersistentFields mechanism to designate serializable fields.unmigrated-wiki-markup

• Finally, because inner classes associated with outer instances do not have zero-argument constructors (constructors of such inner classes implicitly accept the enclosing instance as a prepended parameter), they cannot implement {{Externalizable}}. \[ The {{Externalizable}} interface requires the implementing object to manually save and restore its state using the {{writeExternal()}} and {{readExternal()}} methods.\]

None of these issues, however, apply to static member classes.

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Attempts to serialize inner classes can cause instances of the outer class to be serialized and also introduce platform dependencies.

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