Since CodeNarc 0.19
Checks for enums that define writeObject() or writeReplace() methods, or declare serialPersistentFields or serialVersionUID fields, all of which are ignored for enums.
From the javadoc for ObjectOutputStream:
The process by which enum constants are serialized cannot be customized; any class-specific writeObject and writeReplace methods defined by enum types are ignored during serialization. Similarly, any serialPersistentFields or serialVersionUID field declarations are also ignored--all enum types have a fixed serialVersionUID of 0L.
Example of violations:
enum MyEnum {
ONE, TWO, THREE
private static final long serialVersionUID = 1234567L // violation
private static final ObjectStreamField[] serialPersistentFields = // violation
{ new ObjectStreamField("name", String.class) }
String name;
Object writeReplace() throws ObjectStreamException { .. } // violation
private void writeObject(ObjectOutputStream stream) { .. } // violation
}
New in CodeNarc 0.14
To use a Serializable object's serialPersistentFields correctly, it must be declared private, static, and final.
The Java Object Serialization Specification allows developers to manually define Serializable fields for a class by specifying them in the serialPersistentFields array. This feature will only work if serialPersistentFields is declared as private, static, and final. Also, specific to Groovy, the field must be of type ObjectStreamField[], and cannot be Object.
References:
Example of violations:
class MyClass implements Serializable {
public ObjectStreamField[] serialPersistentFields = [ new ObjectStreamField("myField", List.class) ] as ObjectStreamField[]
}
// the JVM sees the field type as Object, which won't work
class MyOtherClass implements Serializable {
private static final serialPersistentFields = [ new ObjectStreamField("myField", List.class) ] as ObjectStreamField[]
}
Since CodeNarc 0.11
A serialVersionUID is normally intended to be used with Serialization. It needs to be of type long, static, and final. Also, it should be declared private. Providing no modifier creates a Property and Groovy generates a getter, which is probably not intended.
From API javadoc for java.io.Serializable: It is also strongly advised that explicit serialVersionUID declarations use the private modifier where possible, since such declarations apply only to the immediately declaring class--serialVersionUID fields are not useful as inherited members.
New in CodeNarc 0.13
Classes that implement Serializable should define a serialVersionUID. Deserialization uses this number to ensure that a loaded class corresponds exactly to a serialized object. If you don't define serialVersionUID, the system will make one by hashing most of your class's features. Then if you change anything, the UID will change and Java won't let you reload old data.
An example of a missing serialVersionUID:
class MyClass imlements Serializable {
// missing serialVersionUID
}