RE: HTML to XML, vice versa

On 03/19/2001 at 08:17:29 AM, owner-java400-l@midrange.com wrote:
How does this differ from what Fred explained?  Are there pros, cons, or
are
they the same?  When you say "subclass a class" I assume you mean to define
the one Formatter class, then for the XML and HTML classes, "extend" the
original formatter class.

The 'interface' and 'implements' is java's solution to the
evils of multiple inheritence.
I use interfaces and containment more frequently than
inheritence.

Abstract classes and abstract methods can get you in a jam,
because if you've got your class extending a class.
Since you can only extend ONE class (single inheritence), this
can get you into a design quandery sometimes.
Also, you start tending to use inheritence as a mechanism for
code reuse, and that is a BAD use for inheritence.
Encapsulation should be used for that.


So, if you want to use some code from another class BASE and you
want your object to be an instance of that class, then restructure
into interfaces and use 'implements'.

/* Class that seems abstract but still does some useful stuff. */
class Base {
   public void foo() {
      // Method with useful logic
   }
   public abstract void bar();
   public abstract void bazzle();
}

class MyClass extends BASE {
  // I try to stay away from this.
}

/////// Instead, you can go this route.

interface Base {
   public void foo();
   public void bar();
   public void bazzle();
}

// A common programming model is to call
// this class 'BaseImpl'.
class BaseHelper {
   public void foo() {
      // Method with useful logic
   }
   // You COULD make this implement Base if
   // you wanted, but its really only intended
   // to provide help for a subset of the
   // behavior foo() provides and thus
   // DOESN'T logically implement Base.
   // We don't want to use inheritence or
   // implementation to do code reuse, so
   // we make sure it doesn't physically either,
}

class MyClass implements Base {
   BaseHelper  bh = new BaseHelper();

   public void foo() {
       bh.foo();
   }
   // As more stuff becomes factored out in
   // your multiple implementations of 'Base',
   // you may find that behavior from
   // those multiples migrate to BaseHelper
   // and are common.
   public void bar() {
      // implementation
   }
   public void bazzle() {
      // implementation
   }
}



"The stuff we call "software" is not like anything that human society
  is used to thinking about. Software is something like a machine, and
  something like mathematics, and something like language, and
  something like thought, and art, and information...
  but software is not in fact any of those other things."
Bruce Sterling - The Hacker Crackdown

Fred A. Kulack  -  AS/400e  Java and Java DB2 access, Jdbc, JTA, etc...
IBM in Rochester, MN  (Phone: 507.253.5982   T/L 553-5982)
mailto:kulack@us.ibm.com   Personal: mailto:kulack@bresnanlink.net
AOL Instant Messenger: Home:FKulack  Work:FKulackWrk

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