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    <p>have a few questions in the above example.</p> <ol> <li><p><em>When to use flush method and why do we use it?</em></p> <p>You usually won't need to <code>flush()</code> and <code>OutputStream</code>, it won't lose any data if you properly <code>close()</code> it in the end. Sometimes, you want to communicate to the underlying data sink (e.g. network <code>Socket</code>, local <code>File</code>, or another <code>OutputStream</code>) that you want any data written to the stream to be flushed/processed -- but as per the <a href="http://download.oracle.com/javase/6/docs/api/java/io/OutputStream.html#flush%28%29" rel="nofollow"><code>flush()</code></a> API doc, that's <strong>not guaranteed</strong> to happen.</p></li> <li><p><em>What does close method carry a score here?</em></p> <p>I really don't understand this part, but the <code>close()</code> closes an <code>OutputStream</code> and causes it to write out any data it still has buffered -- so there's no need to call <code>flush()</code> before <code>close()</code>. An <code>OutputStream</code> can not be written to after it has been closed.</p></li> <li><p><em><code>myObj2 = (John) ois.readObject();</code> ... please correct me if i am wrong, i am reading the file object and storing into another object and typecasting the file object.</em></p> <p>Wrong, you're reading from the <code>ObjectInputStream</code> <code>ois</code>, it's irrelevant where it has its data from (in your case it does, indeed, come from a file, but there's no "file object" in your code). </p> <p><code>ObjectInputStream</code> can reconstruct any data previously written/serialized by <code>ObjectOutputStream</code> -- so in this case you <strong>de-serialize</strong> a previously serialized object of type <code>John</code>. Because serialization only works on some Java types (primitives and implementors of <code>Serializable</code>), it doesn't know about your specific class <code>John</code>. But you know, you previously serizalized a <code>John</code> object, so you can safely cast from <code>Object</code> to <code>John</code> and assign it to a local variable.</p></li> <li><p><em>What are the alternatives of Serialization or persisting the data in Java. I don't want the data to get into file as byte stream.</em></p> <p>You could look into other serialization/marshalling approaches like <a href="http://xstream.codehaus.org/" rel="nofollow">XStream</a>, <a href="http://www.json.org/java/index.html" rel="nofollow">JSON</a> or roll your own (complex, only do this if you have a good reason). Most of these will prove more complex than the built-in serialization, so be sure you have a good reason to not just write "itno file as byte stream".</p></li> </ol>
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    1. POWhen to use flush() in java?
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    1. USPhilipp Reichart
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    1. COAre you sure (2) is correct? Where does the API for close() guarantee that all outstanding bytes will be flushed?
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      1. USPaul Grime
    2. COThere's little documentation, mostly personal experience -- most streams will `flush()` on closing them, like [FilterOutputStream](http://download.oracle.com/javase/6/docs/api/java/io/FilterOutputStream.html#close()) which most others extend and [ObjectOutputStream](http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/io/ObjectOutputStream.java#ObjectOutputStream.close%28%29) and they all dutifully implement `flush()`, with the notably exception of [GZIPOutputStream](http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4813885).
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      1. USPhilipp Reichart
 

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