Moderator (MDR): MDR-Andrea

Guest-Speaker (SPK): SPK-regman

MDR-Andrea: Hello and welcome to Java Live. Today's topic is the JavaBeans^TM Developement Kit (BDK). Our guest is BDK engineer Reggie Adkins. Go ahead and start sending in your questions and we'll start through them. Thanks for joining!

snarayanan: How are JavaBeans components used with Communicator or IE? Netscape supports something called Bean connect, while IE dosen't support it. So do I wrap my Bean in an applet and use it in the browser?

SPK-regman:

1. You could wrap the Bean in an applet.
2. You could use the Java^TM Plug-in (formerly known as Project Java^TM Activator).

JamieS: If I've defined a nice GUI customizer for a JavaBean component, should I bother to expose its getter/setter methods in the BeanInfo class? Do you think that this redundancy would be helpful, or merely confusing?

SPK-regman: Good question. Well, let's see. Builder tools, ideally, will always use your customizer. However, if for some reason it does not, you might still want to be able to use your Bean (or for someone else to use it) in a builder tool that only uses property sheets. I would go for redundancy.

RefuX: I program Java apps, but I have no idea what Beans are. What are they? :)

SPK-regman: JavaBeans are reusable software components that can be visually manipulated in a builder tool. See http://java.sun.com/beans for much more detail. There is a Beans Development Kit (BDK) there that you can download, which will get you started.

JamieS: Is Bean introspection information cached by the Introspector, or should I maintain a Bean Class <-> Customizer Class table for frequently used classes?

SPK-regman: The Introspector does cache some information. I don't recall what it specifically caches off-hand, other than BeanInfo's.

q3: I'm a Java programming newcomer. Does using a JavaBean component in my design affect the overall efficiency of my application?

SPK-regman: No, JavaBeans are implemented in the Java programming language. There is nothing new to learn (except for some coding conventions outlined in the spec), and everything on the Java Platform is available to you.

JamieS: Is the BeanBox being updated (as sample code)? Should I expect a BeanBox that uses the 1.2 Bean features (contexts, Swing, etc.) at some point? Thanks.

SPK-regman: Yes. The BeanBox is being updated. We will have a version with 1.2 support for BeanContexts soon. We are also going to provide Swing, drag and drop, and InfoBus support, appropriate as they come online.

JamieS: If I extend a Bean (i.e. class betterBean extends aBean), do I need to define a BeanInfo for betterBean (probably class betterBeanBeanInfo extends aBeanBeanInfo), or will the beanInfo for aBean be found and applied by the Introspector? The experimenting I've done implies that the Introspector does not look at parent classes, but I figure since you're here I might as well check with the guru.

SPK-regman: The Introspector will look at the parent classes, unless you tell it to stop by providing a stop class. Think of BeanInfo as "overriding" for that hierarchy level.

RefuX: Surely Beans generate huge amounts of unused code, thus bloating Java apps and slowing them down?

SPK-regman: Theoretically, there should be no slow down at all. Also, if you use Beans off-the-shelf and then only use a little bit of the functionality it provides, then yes, you are getting unused code bloat. On the other hand, a well-written Bean will do one thing and do it well so that a good portion of its code is being used when trying to provide its functionality. (Does that make sense?)

39988: Can you recommend a text book for beginners trying to learn JavaBeans?

SPK-regman: Actually, I can't off the top of my head. I recommend looking at our web site. It recommends lots of books. Also, downloading the BDK from http://java.sun.com/beans is where I would start.

MDR-Andrea: Chuckie has informed me that the JavaWorld^TM site (www.javaworld.com) currently has some reviews posted on Beans books. Thanks for the tip.

snarayanan: Why doesn't the event target dialog in the BDK show all the public methods in my Bean? It shows only the methods of my Beans that would take no args or Object class as args. But the behavior of JavaStudio^TM is quite different.

SPK-regman: The BeanBox event target dialog only shows the event targets that are compatible with the event you are trying to connect to the Bean.

snarayanan: This is a continuation of my previous question. Is this a limitation with the BDK? Will the event target dialog also show static methods?

SPK-regman: I have not confirmed that myself, but it should. (Would you like to let us know?) :-)

rickm74: Can you elaborate on the differences between JavaBeans and Enterprise JavaBeans^TM (EJB)?

SPK-regman: EJB has a different event model than JavaBeans. They are used more on the server side.

chuckie: Speaking of JDK^TM 1.2, will there be any differences in Bean support from JDK 1.1 to JDK 1.2? Thanks.

SPK-regman: In JDK 1.2 we will support BeanContexts and BeanContextServices. This will allow a Bean to dynamically get services from its logical container. Also, the design time vs. runtime flag will be information that can be obtained from the logical container as well.

snarayanan: I do not understand the need for InfoBus and how it can be used with BDK.

SPK-regman: InfoBus allows Beans to locate each other in an application and interchange data in a well-defined fashion. You can "plug together" content/data consumers and producers using InfoBus.

tng713: This is more specific to Java programming than JavaBeans. I have been trying to compile two classess which are interdependent of one another. In C++, I can declare one class as a forward declaration variable. Does the Java programming language have something similar to C++? Or do you have any other ways to get around this problem? Thanks for the help.

SPK-regman: There are no issues with forward references that I am aware of.

snarayanan: I am not familiar with JavaStudio. But I would still like to ask another question. Can I use JavaStudio to develop Beans, or is it just connect to the Beans to develop another Bean or app?

SPK-regman: JavaStudio is used primarily to connect existing Beans together to create an application.

snarayanan: I understand that all Swing components are Beans. When I try to use them with BDK, I get exceptions. Any reasons? I don't remember the type of exception ;-(

SPK-regman: The current version of the Swing components do not have a full compliment of Bean customizers and property editors. Hence the BeanBox warns that it cannot find some of them. This may be what you are looking at.

snarayanan: I understand Java Foundation Classes components are Beans themselves. But when I try to use it with BDK, I get exceptions. Any reasons? I tried using JOptionPane and CheckBox.

SPK-regman: Again, because of the lack of property editors and customizers in the BeanBox, the Swing components may not be fully and properly configured while you are trying to use them. Indeed, it may not be possible to configure some using just the BeanBox. This will be fixed in the future. In the meantime, the Swing components are very accessible from a programmatic point of view.

JamieS: I know that some workarounds were provided to Bean GUI environment vendors to help them manipulate the properties of Swing components, because the standard model was not quite sufficient for covering all of the bases. Do you know where I might find more information about this? Thanks.

SPK-regman: Did my last two responses answer your question?

JamieS: I have a question about Beans and JDK 1.2 security. JDK 1.2 security enhancements include a new privilege for the reflection APIs. Does this privilege grant the right to introspect beyond the normal access rights (i.e. to use reflection to access privates, such as for debugging), or does it grant the right to use reflection at all? If this privilege grants the former ability, then it's not really that important (for Beans), but if it controlls the latter, then it would be pretty important to have enabled when using Beans. I've experimented with JDK 1.2 Beta 3 and the reflection APIs, but have not tried running them from a secure environment, like a browser or a 1.2 Activator, so I'm not really sure. Thanks.

SPK-regman: I'm not familiar with the semantics of this priviledge. You could:

1. Run an experiement.
2. Check the Beta 3 docs.

muleman: Hi. There seems to be some confusion between the white papers and tutorials about which parts of a Bean (events, properties, methods) are intended for design-time versus run-time. Any comments? The question I'm really getting at is: For a Bean that could also be a class library, shouldn't one write the class library without regard to the Bean API, but then wrap it in a Bean?

SPK-regman: When you package your Bean in a Java ARchive (JAR) file, you can mark some of the entries as design-time only. This is a hint to builder tools that when they use your Bean in a generated application, anything marked "design-time only" does not need to be included in the final output.

snarayanan: What tool should I use to connect servlet Beans? I understand that JavaServer^TM comes with some tool to deploy Beans, but what if I'm not using JavaServer?

SPK-regman: Sorry, I am not familiar with servlets. You can check the web site. They should also have references to tool vendors.

snarayanan: Sometimes when I design a Bean and load it using BDK, I get a ClassNotFound exception. I am sure all classes are there. If I reinstall BDK, would things would work? Do you know what might be happening?

SPK-regman: The BeanBox is just a tool. It's not meant for formal app development. As such, it does not use the classpath variable (Yes, we know you have taken painstaking efforts to set properly :-) ).

The BeanBox only looks for classes and JARs in a directory local and relative to it. If your classes are not in one of these locations (one escapes me, the other is the JAR's folder), you will get a ClassNotFound exception. You can of course, change the .bat or .sh file to use the classpath you specify. 0 FYI.

SPK-regman: Well, I'll have to think about this, but the first thing I might guess off the top of my head is that the scope of an inner class should be its class only. So, innerA should only exist inside class a. However, because the inner classes are generated as classfiles out in the filesystem, the new mechanism probably picks up the generated class file for the innerA class, when it should not. But this is just my guess. In any case, I will take it back and look at it.

Thanks for the Forum!

MDR-Andrea: Well, we are out of time. Thanks for a lively discussion. Check the schedule for more Java Live forums. In the meantime, take care and I'll see you next time.