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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 +--- | This is the JAVA/400 Mailing List! | To submit a new message, send your mail to JAVA400-L@midrange.com. | To subscribe to this list send email to JAVA400-L-SUB@midrange.com. | To unsubscribe from this list send email to JAVA400-L-UNSUB@midrange.com. | Questions should be directed to the list owner: joe@zappie.net +---
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