But these helper classes all have the same methods and attributes, I would have to define all the methods in all the helper classes like the example code from the previous email. And you are suggesting I do that?
--Stacy ----- Original Message ----- From: Galbreath, Mark To: 'Struts Users Mailing List' Sent: Friday, March 01, 2002 12:45 PM Subject: RE: Digester and inheritance It appears from your listings and descriptions that Component is basically a JavaBean and your helper classes should have "has a" relationships with it, not "is a." Essentially, what I am suggestion is that you wrap Component in the helper classes. Wrappers are far more functional than subclasses (also known as the "decorator" pattern) and ensure that adding methods to Component will never affect the helpers (loose coupling), making ongoing maintenance easier. IMHO, implementation (class) inheritance is way overused in Java (even within the Java API). As for Digester, it is indifferent to the relationships between your classes; I am merely suggesting a refactoring of your code. Mark -----Original Message----- From: Stacy Weng [mailto:[EMAIL PROTECTED]] Sent: Friday, March 01, 2002 3:13 PM To: Struts Users Mailing List Subject: Re: Digester and inheritance Wouldn't that be a "has-a" relationship? If I do that, than I would end up with this (since originally I have many child classes extending from Component): public class Component { public String name = null; public String getName() { return this.name; } public void setName(String name) { this.name=name; } } public class HelperClass1 { private final Component c; public String getName() { return c.getName; } public void setName(String name) { c.setName(name); } } public class HelperClass2 { private final Component c; public String getName() { return c.getName; } public void setName(String name) { c.setName(name); } } public class HelperClass3 { private final Component c; public String getName() { return c.getName; } public void setName(String name) { c.setName(name); } } The reason I'm extending from Component is because these helper classes "is - a" Component. They only have slight variations. Does digester not handle "is-a" relationships? --Stacy ps - Thanks again for taking the time to respond. I can't stress how much I appreciate it. ----- Original Message ----- From: Galbreath, Mark To: 'Struts Users Mailing List' Sent: Friday, March 01, 2002 2:40 PM Subject: RE: Digester and inheritance You are misusing inheritance. Instead of extending Component, give HelperClass (was ChildClass) a private field that references an instance of Component (a design pattern known as "composition").Each instance method in HelperClass invokes the corresponding method on the contained instance of Component and returns the results (a design pattern known as "forwarding"): public class HelperClass { private final Component c; public void setName( String name) { c.setName( name); } public String getName() { return c.getName(); } } Cheers! Mark -----Original Message----- From: Stacy Weng [mailto:[EMAIL PROTECTED]] Sent: Friday, March 01, 2002 2:12 PM I have a parent class called Component, and several child classes extending from it. All the common get/set methods are defined in Component. So, after each child is getting created from addObjectCreate() method, I call addSetProperties() method to initialize their values (values are from the xml file), however, digester can't find the set methods from the child class, cause they're defined in the parent class (Component). The temporary solution I had was defining those set methods in the child classes, and have them call the super methods. But that seems to defeat the whole purpose of inheritance. Here's an example with the problem: public class Component { public String name = null; public void setName(String name) { this.name=name; } public void getname() { return this.name; } } public class ChildClass extend Component { //Other methods that differ from parent class } for the digester rules: digester.addObjectCreate("ChildClassPattern", "some.package.ChildClass"); digester.addSetProperties("ChildClassPattern"); so, as it gets to addSetProperties(), it doesn't see any of the get/set methods in ChildClass, and yet, it doesn't know to look its parent class, Component. I hope I'm able to get my problem across. Thanks again for taking the time to respond. --Stacy ----- Original Message ----- From: Fernando Esteban Barril Otero To: Struts Users Mailing List Sent: Friday, March 01, 2002 1:48 PM Subject: Re: Digester and inheritance I'm using digester and inheritance without problems. What kind of exception are you getting? Fernando ----- Original Message ----- From: "Stacy Weng" <[EMAIL PROTECTED]> To: "Struts Users Mailing List" <[EMAIL PROTECTED]> Sent: Friday, March 01, 2002 1:20 PM Subject: Digester and inheritance Has anyone encountered problems with inheritance using Digester? It seems to me that the addSetProperties() does not when its object is inherited from a parent class...hence it assumes the get/set methods aren't defined, when they are actually defined in its parent class. I've looked into the source, and it seems that the getMethod call that digester uses does not handle parent methods. Is there a patch out there for inheritance with digester? Once again, thanks again in advance for any input. It is greatly appreciated. =) --Stacy -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]> -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]> -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]>
