[ajug-members] correct interface programming
Wilson, Jeff
jw9615 at att.com
Fri Jul 25 15:31:31 EDT 2008
You got it right.
+jeff (MJW)
---
"Sarchasm: The gulf between the author of sarcastic wit and the
recipient who doesn't get it."
---------------------------------------------
M. Jeff Wilson, Lead Member Technical Staff
AT&T Services, Inc.
Operations & Service Dev
jw9615 at att.com
+1 404.499.7235
From: 521 [mailto:521 at ofig.org]
Sent: Friday, July 25, 2008 3:14 PM
To: ajug-members at ajug.org
Subject: Re: [ajug-members] correct interface programming
J.Wilson: in other words, for me (a newbe), the Growable interface must
only define methods(actions) that are related to growing, wether it be a
crystal or a tree; but what if they grow in a different fasion? say a
tree or a crystal... the Growable interface does not define how
something grows? it only supplies a GrowRate method and a getCurrentSize
method or the like...? am i saying this correctly?
barclay
On Fri, 25 Jul 2008 14:46:49 -0400, Wilson, Jeff wrote
> Of course, the real point of interfaces is to allow a client to only
depend on the methods declared in that one interface and not care about
the actual implementation.
>
> For example, I can use the Growable interface with something that is
neither a Plant or a Tree:
>
> public class Crystal implements Growable {
> public double getGrowthRate() { return 0.023; }
> public Dimension getCurrentSize() { return new Dimension (1.2, 3.0);
}
> }
>
> Now I can write a class that predicts the sizes of any thing that
implements Growable:
>
> public class GrowthPredictor {
> public Dimension predictSize(int numberOfPeriods, Growable growable)
{
> double width = growable.getCurrentSize().width();
> double height = growable.getCurrentSize().height();
> double factor = numberOfPeriods * growable.getGrowthRate();
> width += (width * factor);
> height += (height * factor);
>
> return new Dimension(width, height);
> }
> }
>
> This new class doesn't care how many interfaces its argument
(growable) implements, as long as it implements the Growable interface.
This method can be compiled without having any access to Tree or Crystal
-- it isn't bound to the class, but the interface. In fact, this class
can be compiled before Tree and Crystal classes even exist, and it will
work just fine when, in the future, you pass it a Tree or a Crystal.
>
> +jeff (MJW)
> ---
>
> "Foreploy: Any misrepresentation about yourself for the purpose of
obtaining sex."
>
> ---------------------------------------------
> M. Jeff Wilson, Lead Member Technical Staff
> AT&T Services, Inc.
> Operations & Service Dev
> jw9615 at att.com
> +1 404.499.7235
>
> > -----Original Message-----
> > From: Wilson, Jeff
> > Sent: Thursday, July 24, 2008 4:54 PM
> > To: ajug-members at ajug.org
> > Subject: Re: [ajug-members] correct interface programming
> >
> > Here's some perfectly valid code:
> >
> > public interface Growable {
> > double getGrowthRate();
> > Dimension getCurrentSize();
> > }
> >
> > public interface Shady {
> > boolean isInShade(Point pt);
> > }
> >
> > public interface LumberSource {
> > double getPotentialBoardFeet();
> > boolean isReadyToCut();
> > }
> >
> > public class Tree extends Plant implements Growable, Shady,
LumberSource {
> > private double width;
> > private double height;
> >
> > public Dimension getCurrentSize() { return new Dimension(width,
height); }
> > public boolean isInShade(Point pt) { return false; }
> > public double getPotentialBoardFeet() { return 2000.0; }
> > public boolean isReadyToCut() { return false; }
> > }
> >
> > public class Plant {
> > public double getGrowthRate() { return 0.42; }
> > }
> >
> > No, Tree can implement any number of interfaces, there is no limit.
> >
> > Yes, Tree must have a method declaration for every method in all if
the interfaces. HOWEVER, a method declared in a
> > subclass of Tree with the same signature as a method in one of
Tree's interfaces satisfies that contract. For
> > example, in the code above, the getGrowthRate() method of the
Growable interface is met by the Plant class. That is
> > perfectly valid.
> >
> > Yes, by implementing an interface, this is a contract -- the
compiler will force you to have a method for every
> > method in an interface your class implements, either in the class or
one of its parent classes.
> >
> >
> >
> > +jeff (MJW)
> > ---
> >
> > "Foreploy: Any misrepresentation about yourself for the purpose of
obtaining sex."
> >
> > ---------------------------------------------
> > M. Jeff Wilson, Lead Member Technical Staff
> > AT&T Services, Inc.
> > Operations & Service Dev
> > jw9615 at att.com
> > +1 404.499.7235
> > > -----Original Message-----
> > > From: 521 [mailto:521 at ofig.org]
> > > Sent: Thursday, July 24, 2008 3:43 PM
> > > To: ajug-members at ajug.org
> > > Subject: [ajug-members] correct interface programming
> > >
> > > am i saying this correctly?, that which is below... -barclay
> > >
> > > {{{
> > > if i program to an interface, i do not have to worry about the
number of
> > > interfaces that are implemented, do i? but do i not have to use
all methods
> > > in an implemented interface? i do have to- it's a contract.
correct? and
> > > because you can only extend one class, you have no contract there.
correct?
> > > can someone see what my question is?
> > >
> > > a tree; a tree can grow, a tree can provide shade; and a tree can
provide
> > > lumber for table-tennis.
> > >
> > > so my tree class is designed...
> > >
> > > then if i am implementing a 'tree'- it depends on which
implementation i use
> > > thus have a contract to use certain methods
> > > }}}
> > >
> > >
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