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POfinal transient fields and serialization
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  1. POfinal transient fields and serialization
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    copied!<p>Is it possible to have <code>final transient</code> fields that are set to any non-default value after serialization in Java? My usecase is a cache variable — that's why it is <code>transient</code>. I also have a habit of making <code>Map</code> fields that won't be changed (i.e. contents of the map is changed, but object itself remains the same) <code>final</code>. However, these attributes seem to be contradictory — while compiler allows such a combination, I cannot have the field set to anything but <code>null</code> after unserialization.</p> <p>I tried the following, without success:</p> <ul> <li>simple field initialization (shown in the example): this is what I normally do, but the initialization doesn't seem to happen after unserialization;</li> <li>initialization in constructor (I believe this is semantically the same as above though);</li> <li>assigning the field in <code>readObject()</code> — cannot be done since the field is <code>final</code>.</li> </ul> <p>In the example <code>cache</code> is <code>public</code> only for testing.</p> <pre><code>import java.io.*; import java.util.*; public class test { public static void main (String[] args) throws Exception { X x = new X (); System.out.println (x + " " + x.cache); ByteArrayOutputStream buffer = new ByteArrayOutputStream (); new ObjectOutputStream (buffer).writeObject (x); x = (X) new ObjectInputStream (new ByteArrayInputStream (buffer.toByteArray ())).readObject (); System.out.println (x + " " + x.cache); } public static class X implements Serializable { public final transient Map &lt;Object, Object&gt; cache = new HashMap &lt;Object, Object&gt; (); } } </code></pre> <p>Output:</p> <pre><code>test$X@1a46e30 {} test$X@190d11 null </code></pre>
 

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