readObject

The readObject method in Java is a special method used within the Serialization mechanism. It's part of the java.io.Serializable interface and is invoked when an object is deserialized from a stream. This method allows a class to customize the deserialization process for its instances.

If a class implements the readObject method, it takes over the responsibility of reading its own state from the input stream, overriding the default mechanism that uses reflection to find and set fields. This is particularly useful for handling transient fields, managing complex object graphs, or performing validation during deserialization.

The signature of the readObject method must be public void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException. The ObjectInputStream parameter provides access to the serialized data. Inside the method, developers typically use methods like in.readObject(), in.readInt(), in.readUTF(), etc., to read the fields of the object in the same order they were written by the corresponding writeObject method.

It is crucial that the readObject method is correctly implemented. Mismatches in reading data compared to writing data can lead to corrupted objects or runtime errors. If a class does not define its own readObject method, the default deserialization process will be used, which involves matching field names and types between the serialized data and the class definition. The readResolve method can also be used in conjunction with readObject to replace the object being deserialized with another object, often a singleton instance.