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close() method; I/O class chaining

 
Ram Manoj
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From K&B book
Whenever you're done using a file, either reading it or writing
to it, you should invoke the close() method.


But when using chaining with I/O classes is invoking the close() method on the Top wrapped class like PrintWriter or BufferedReader sufficient.
How does the mechanism of close() work when chaining?

 
Marco Ehrentreich
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Hi Ram,

in your example you have a PrintWriter wrapping a BufferedWriter wrapping a FileWriter.

Because of this it's sufficient to call close() on the outermost I/O object (PrintWriter) and this one will call close() on the writer it has wrapped which in turn will call close() on the writer it has wrapped and so on until the end of the chain (the innermost writer = FileWriter).

Marco
 
Ram Manoj
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Thanks Mark.

This's been a long lasting doubt for me.

Can you point to a link related to this.
 
Marco Ehrentreich
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Unfortunately I don't find a really good link at the moment which explains the chaining of Java I/O classes.

Perhaps this Wikipedia article about the decorator pattern may enlighten you. It doesn't describe the Java I/O classes at all, but it's effectively the decorator design pattern which is used when wrapping one object with another as in the case with the Java I/O classes. This and related links hopefully may help you to better understand the concept behind this.

Marco
 
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