To initialize a transient field, what is the most simple solution

Question

class MyClass implements Serializable {
  transient int myTransient;
  //Other variables
}

When I restore this class I want to initialize myTransient manually, but otherwise I just want to use the default serialization.

How can I inject an init() method into the object restore process without re-writing the entire serialization mechanism as it seems like Externalizable would have me do?

Answer 1

Implement a readObject() method:

private void readObject(java.io.ObjectInputStream in)
    throws IOException, ClassNotFoundException {
    in.defaultReadObject();
    myTransient = ...;
}

From javadoc:

Classes that require special handling during the serialization and deserialization process must implement special methods with these exact signatures:

private void readObject(java.io.ObjectInputStream in) throws IOException, ClassNotFoundException;

The readObject method is responsible for reading from the stream and restoring the classes fields. It may call in.defaultReadObject to invoke the default mechanism for restoring the object's non-static and non-transient fields. The defaultReadObject method uses information in the stream to assign the fields of the object saved in the stream with the correspondingly named fields in the current object. This handles the case when the class has evolved to add new fields. The method does not need to concern itself with the state belonging to its superclasses or subclasses. State is saved by writing the individual fields to the ObjectOutputStream using the writeObject method or by using the methods for primitive data types supported by DataOutput.

See also:

• Serializable javadoc