[Chapter 7] Object Serialization

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| Chapter 7 |

# 7. Object Serialization

Contents:
Object Serialization Basics
Writing Classes to Work with Serialization
Versioning of Classes

The object serialization mechanism in Java 1.1 provides a way for objects to be written as a stream of bytes and then later recreated from that stream of bytes. This facility supports a variety of interesting applications. For example, object serialization provides persistent storage for objects, whereby objects are stored in a file for later use. Also, a copy of an object can be sent through a socket to another Java program. Object serialization forms the basis for the remote method invocation mechanism in Java that facilitates distributed programs. Object serialization is supported by a number of new classes in the `java.io` package in Java 1.1.

## 7.1 Object Serialization Basics

If a class is designed to work with object serialization, reading and writing instances of that class is quite simple. The process of writing an object to a byte stream is called serialization. For example, here is how you can write a `Color` object to a file:

    FileOutputStream out = new FileOutputStream("tmp");
    ObjectOutput objOut = new ObjectOutputStream(out);
    objOut.writeObject(Color.red);

All you need to do is create an `ObjectOutputStream` around another output stream and then pass the object to be written to the `writeObject()` method. If you are writing objects to a socket or any other destination that is time-sensitive, you should call the `flush()` method after you are finished passing objects to the `ObjectOutputStream`.

The process of reading an object from byte stream is called deserialization. Here is how you can read that `Color` object from its file:

    FileInputStream in = new FileInputStream("tmp");
    ObjectInputStream objIn = new ObjectInputStream(in);
    Color c = (Color)objIn.readObject();

Here all you need to do is create an `ObjectInputStream` object around another input stream and call its `readObject()` method.

File Manipulation |  | Writing Classes to Work with Serialization