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For the simplicity of writing a lot and also boring you guys I just have a question and if you guys can give me another example as well using maybe something simpler.

Here is the code

PrinterWriter w = new PrinterWriter(new FileWriter("test.txt"));

ok so the above works perfectly fine but so does this 

FileWriter fw = new FileWriter("test.txt");

So does this work

PrintWriter w = PrintWriter(new File("test.text");

Ok so now all of these work but I am more concerned on why does the one in italics work.

I have read some of the documentation and have noticed that it takes a Writer as the constructor argument, which FileWriter is an extension of.

But if that is true then why does this not work (or maybe it does)

FileWriter fw = FileWriter(new PrintWriter("test.txt));

I have not yet confirmed if this works but I do not see what this would do anyways ( the others make sense ) but can anyone just explain even the slightest bit of information?

user207421
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user3453661
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1 Answers1

1

Java uses the Decorator pattern to provide specialized combinations of Writer/Stream

  • Writer an object you can write characters to
  • PrintWriter specialized Writer that provides formating options, like linebreaks (e.g. println()) or `printf`` aso
  • OutputStream an object to write bytes to

So:

A FileWriter("test.txt") is an object you can write characters to, that are written to a file.

A PrintWriter(new FilteWriter("test.txt")) is an object that provides formatting options, that writes characters to an object that writes to a file.

A PrintWriter(new File("test.txt")) is semantically the same, a writer with formatting options that writes characters to a file. (just without an extra step)

FileWriter fw = FileWriter(new PrintWriter("test.txt)); does not compile.

Two other common Writers are the BufferedWriter StringWriter. The BufferedWritero ptimizes for larger chunks of writes, it only writes to the underlying Writer if the buffer is full or flushed. StringWriter is the basic "in memory" implementation that appends to a String.

With that: BufferedWriter( new PrintWriter( new FileWriter("test.txt")));" a chunk based writer with no formatting options, that uses a PrintWriter and FileWriter to write characters to a file.

k5_
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