API Contents - SCJP Sun Certified Programmer for Java Platform SE6 - page 301

The Console class is preferred over using System.out and System.in
when working with formatted output to the console or console input from
the user. Because the class is new in Java 6.0, expect a question or two
about Console on the exam.
Next we discuss a different exam objective: object serialization. I explain how it works
in the next section and discuss the various classes and interface involved.
Object Serialization
The exam objectives state that you need to be able to “develop code that serializes and/or
de-serializes objects using the following APIs from java.io : DataInputStream , DataOutput-
Stream , FileInputStream , FileOutputStream , ObjectInputStream , ObjectOutputStream
and Serializable .” In other words, you need to understand the details of Java object seri-
alization. The earlier section titled “The DataInputStream and DataOutputStream Classes”
discussed saving the state of an object using DataInputStream and DataOutputStream . This
section focuses on the ObjectInputStream and ObjectOutputStream classes and the Serial-
izable interface.
Object serialization refers to taking the state of an object and writing it to a stream.
You can use serialization to persistently store your objects in fi les. You can also serial-
ize an object and send it across the network to another Java program or save it in a data-
base. Deserialization refers to the process of reading the data from an object stream and
reconstituting the object in memory. Not all objects can be serialized; only objects whose
classes implement the java.io.Serializable interface . Let's take a look at this interface
and what it means to implement it.
The Serializable Interface
The Serializable interface is a tagging interface, which means it does not have any meth-
ods in it. A class implements Serializable to let the JVM know that instances of the class
can be serialized. There is no extra work on your part to make a class serializable because
there are no methods in the interface. Your main concern with implementing Serializ-
able is ensuring that all the fi elds in your class are also Serializable . If an attempt is
made to serialize an object and a fi eld is reached during the serialization process that is not
serializable, the JVM throws a NotSerializableException and the serialization fails. The
compiler does not verify whether or not your fi elds are Serializable . Denote a fi eld as
transient (using the transient keyword) to tell the JVM to ignore the fi eld during the seri-
alization and deserialization process.