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Why InputStream Design Is Wrong
It's not just about
InputSteam, this class is a good
example of a bad design. I'm talking about three overloaded
read(). I've mentioned this problem in Section 2.9
of Elegant Objects. In a few words,
I strongly believe that interfaces must be "functionality poor."
InputStream should have been an interface in the first place
and it should have had a single method
read(byte). Then if
its authors wanted to give us extra functionality, they should have
created supplementary "smart" classes.
This is how it looks now:
What's wrong? It's very convenient to have the ability to read a single byte, an array of bytes or even an array of bytes with a direct positioning into a specific place in the buffer!
However, we are still lacking a few methods: for reading the bytes and
immediately saving into a file, converting to a text with a selected
encoding, sending them by email and posting on Twitter. It would be
great to have the features too, right in the poor
I hope the Oracle Java team is working on them now.
In the mean time, let's see what exactly is wrong with what these
bright engineers designed for us already. Or maybe let me show
how I would design
InputStream and we'll compare:
This is my design. The
InputStream is responsible for reading
bytes from the stream. There is one single method for this
feature. Is it convenient for everybody? Does it read and post
on Twitter? Not yet. Do we need that functionality? Of course we do,
but it doesn't mean that we will add it to the interface. Instead,
we will create supplementary "smart" class:
Now, we want to read a single byte from the stream. Here is how:
The functionality of reading a single byte is outside of
because this is not its business. The stream doesn't need to know
how to manage the data after it is read. All the stream
is responsible for is reading, not parsing or manipulating afterwards.
Interfaces must be small.
Obviously, method overloading in interfaces is a code smell. An interface with more than three methods is a good candidate for refactoring. If methods overload each other—it's serious trouble.
Interfaces must be small!
You may say that the creators of
InputStream cared about performance, that's
why allowed us to implement
read() in three different forms. Then I have
to ask again, why not create a method for reading and immediately post it
on Twitter? That would be fantastically fast. Isn't it what we all want?
A fast software which nobody has any desire to read or maintain.