What is a serialVersionUID and why should I use it?

java, serialization, serialversionuid

Solution

The docs for `java.io.Serializable` are probably about as good an explanation as you'll get:

The serialization runtime associates with each serializable class a version number, called a `serialVersionUID`, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization. If the receiver has loaded a class for the object that has a different `serialVersionUID` than that of the corresponding sender's class, then deserialization will result in an `InvalidClassException`. A serializable class can declare its own `serialVersionUID` explicitly by declaring a field named `serialVersionUID` that must be static, final, and of type `long`:

ANY-ACCESS-MODIFIER static final long serialVersionUID = 42L;

If a serializable class does not explicitly declare a `serialVersionUID`, then the serialization runtime will calculate a default `serialVersionUID` value for that class based on various aspects of the class, as described in the Java(TM) Object Serialization Specification. However, it is strongly recommended that all serializable classes explicitly declare `serialVersionUID` values, since the default `serialVersionUID` computation is highly sensitive to class details that may vary depending on compiler implementations, and can thus result in unexpected `InvalidClassExceptions` during deserialization. Therefore, to guarantee a consistent `serialVersionUID` value across different java compiler implementations, a serializable class must declare an explicit `serialVersionUID` value. 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.

Problem

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