Using of object in the interface reference...

I assume you're asking why if:

interface X {}

class B implements X {}

then it's good to do this:

X aVar = new B();

as opposed to:

B aVar = new B();

It's good because it encourages code that defines what a code does as opposed to how it does it. Or to put it another way, it results in designs that are about abstract types and not specific implementations. This generally results in more flexible code.

But note:

1) you're not really "storing" the B object in aVar; aVar is just a reference to an object of B.

2) the above example isn't the best example of coding to an interface. A better example is something like return values or parameters. That is to say, given the above example:

X aMethod() {}

is better than

B aMethod() {}

and

void anotherMethod(X param);

is better than

void anotherMethod(B param);

The difference is more significant here, because the flexibly is reflected in the API and thus the larger design. Whereas, the type of a local variable or a (hopefully private) field is basically an implementation detail.

paulcwa at 2007-7-12 22:18:58 >