Java provides a mechanism, called object serialization where an object can be represented as a sequence of bytes that includes the object’s data as well as information about the object’s type and the types of data stored in the object.
After a serialized object has been written into a file, it can be read from the file and deserialized that is, the type information and bytes that represent the object and its data can be used to recreate the object in memory.
Most impressive is that the entire process is JVM independent, meaning an object can be serialized on one platform and deserialized on an entirely different platform.
Notice that for a class to be serialized successfully, two conditions must be met:
The class must implement the java.io.Serializable or java.io.Externalizable interface.
All of the fields in the class must be serializable. If a field is not serializable, it must be marked transient.
Objects to be stored and retrieved frequently refer to other objects. Those other objects must be stored and retrieved at the same time to maintain the relationships between the objects. When an object is stored, all of the objects that are reachable from that object are stored as well.
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