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copied!<p>You can think of serialization as the process of converting an object instance into a sequence of bytes (which may be binary or not depending on the implementation).</p> <p>It is very useful when you want to transmit one object data across the network, for instance from one JVM to another.</p> <p>In Java, the serialization mechanism is built into the platform, but you need to implement the <em>Serializable</em> interface to make an object serializable.</p> <p>You can also prevent some data in your object from being serialized by marking the attribute as <em>transient</em>.</p> <p>Finally you can override the default mechanism, and provide your own; this may be suitable in some special cases. To do this, you use one of the <a href="https://stackoverflow.com/questions/15496/hidden-features-of-java/142676#142676">hidden features in java</a>.</p> <p>It is important to notice that what gets serialized is the "value" of the object, or the contents, and not the class definition. Thus methods are not serialized.</p> <p>Here is a very basic sample with comments to facilitate its reading:</p> <pre><code>import java.io.*; import java.util.*; // This class implements "Serializable" to let the system know // it's ok to do it. You as programmer are aware of that. public class SerializationSample implements Serializable { // These attributes conform the "value" of the object. // These two will be serialized; private String aString = "The value of that string"; private int someInteger = 0; // But this won't since it is marked as transient. private transient List<File> unInterestingLongLongList; // Main method to test. public static void main( String [] args ) throws IOException { // Create a sample object, that contains the default values. SerializationSample instance = new SerializationSample(); // The "ObjectOutputStream" class has the default // definition to serialize an object. ObjectOutputStream oos = new ObjectOutputStream( // By using "FileOutputStream" we will // Write it to a File in the file system // It could have been a Socket to another // machine, a database, an in memory array, etc. new FileOutputStream(new File("o.ser"))); // do the magic oos.writeObject( instance ); // close the writing. oos.close(); } } </code></pre> <p>When we run this program, the file "o.ser" is created and we can see what happened behind.</p> <p>If we change the value of: <strong>someInteger</strong> to, for example <strong>Integer.MAX_VALUE</strong>, we may compare the output to see what the difference is.</p> <p>Here's a screenshot showing precisely that difference:</p> <p><img src="https://i.stack.imgur.com/oIVA5.png" alt="alt text"></p> <p><em><sub>Can you spot the differences? ;)</sub></em></p> <p>There is an additional relevant field in Java serialization: The <a href="http://www.google.com/search?q=serialversionUID" rel="noreferrer">serialversionUID</a> but I guess this is already too long to cover it.</p>

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