Re: Why Generics?

I wrote:

> OTOH, if you use your own implementation of the type-safe enum pattern,
> then their object-nature is not hidden by the compiler and so you can use
> polymorphism to avoid having to use switch statements in the first place.

I must correct myself. It /is/ possible to define methods against enums
(considered as a special kind of class). I'm not sure how I missed it, but
miss it I did.

The documentation that ships with JDK1.5.0 has a few examples, one shows that
enums can have their own methods (and data too though that's not shown here):

==============
public enum Operation {
PLUS, MINUS, TIMES, DIVIDE;

// Do arithmetic op represented by this constant
double eval(double x, double y){
switch(this) {
case PLUS: return x + y;
case MINUS: return x - y;
case TIMES: return x * y;
case DIVIDE: return x / y;
}
throw new AssertionError("Unknown op: " + this);
}
}
==============

Another demonstrates so-called 'constant specific methods':

==============
public enum Operation {
PLUS { double eval(double x, double y) { return x + y; } },
MINUS { double eval(double x, double y) { return x - y; } },
TIMES { double eval(double x, double y) { return x * y; } },
DIVIDE { double eval(double x, double y) { return x / y; } };

// Do arithmetic op represented by this constant
abstract double eval(double x, double y);
}
==============

-- chris


.

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