DataOutputStream（）VS DataOutputStream（new BufferedOutputStream（））

Question

The code at Java Tutorials showed an example of using DataOutputStream class and DataInputStream class.

A snippet of the code looks like this:

//..
out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(dataFile)));
//..
in = new DataInputStream(new BufferedInputStream(new FileInputStream(dataFile)));
//..

I was wondering why is it required to create a new BufferedOutputStream when we create a new DataOutputStream ?

Isn't it redundant since this alternative works as well? : new DataOutputStream(new FileOutputStream(dataFile));

As this page claims, DataStreams already provides a buffered file output byte stream. So is "double-buffering" really required?

I've modified the 2 lines of code (output and input), taking away the BufferedOutputStream and BufferedInputStream and everything seems to work just fine, so I was wondering what is the purpose of the BufferedOutputStream and BufferedInputStream ?

Answer 1

Wrapping the FileOutputStream in a BufferedOutputStream will generally speed up the overall output of your program. This will only be noticeable if you are writing large amounts of data. The same thing goes for wrapping an InputStream in a BufferedInputStream. The use of buffers will only affect efficiency, not correctness.

Answer 2

It's not redundant, it's just different. The Buffered variants add a buffering layer, speeding up IO operations by batching up reads and writes.

Instead of going to disk for every read/write, it goes to memory first. How much of a difference it makes depends on a variety of factors. The OS and/or disk I/O system also likely does some buffering.

Answer 3

I used to think that the Java IO model was unnecessarily large, but now that I really "get it" I find it quite elegant. A BufferedOutputStream is an implementation of the Decorator pattern (google it... it's useful). What this means is that BufferedOutputStream simply adds functionality to the outputstream it wraps. Internally, the BufferedOutputStream calls what ever OutputStream it decorates.

Answer 4

Buffered IO streams help you to read in bulk thereby reducing the IO cost significantly. IO perations are fairly costly. Imagine your application doing a full read/write cycle for every byte that is read/written as opposed to reading/writing a chunk of data in one go. Doing a Buffered read/write is definitely very efficient. You will notice a huge difference in efficiency if you gather some performance statistics in both the cases ie w and w/o Buffered IO specially when reading/writing a huge amount of data.