Difference between Java class and JavaBean?

What is the difference between a Java class and a JavaBean?
A class has variables which hold state.
A class has methods which can do things (like change state).
And if I understand a JavaBean it is rather like a BIG class...
i.e.
A JavaBean has variables which hold state.
A JavaBean has methods which can do things (like change state).
So, what's the difference between the two?
And in case it helps...What is the crossover point between the two? Is there a minimalist type JavaBean which is the same as a class? What is the difference between Java beans and Enterprise Java Beans?
Thanks.

Introspection, as I understand it is a bunch of
methods which allows me to ask what a class can do
etc. right? So, if I implement a bunch of
introspection methods for my class then my class
becomes a JavaBean?Introspection allows a builder tool to discover a Bean's properties, methods, and events, either by:
Following design patterns when naming Bean features which the Introspector class examines for these design patterns to discover Bean features.
By explicitly providing the information with a related Bean Information class (which implements the BeanInfo interface).
I understand now they are completely different.
Thanks. Very clear.
I do not understand how they are completely different.
In fact I don't have a clue what the differences are
other than to quote what you have written. In your
own words, what is the difference? This is the "New
to Java Technology" forum ;-) and I'm new to these
things.In that case ejbs are way too advanced for you, so don't worry about it.

Similar Messages

What is the difference between Abstract class and Interface ?

Hi,
Could u plz tell me the difference between Abstract class and Interface?
Thanks in advance.
Gopi

Lots.
An abstract class can contain some method implementations, or indeed all the method implementations. It may contain methods with all the various access modifiers. It cannot be instantiated. A class may inherit from only a single abstract class.
An interface contains only public method stubs and constants. A class may implement multiple interfaces. An interface cannot (obviously) be instantiated.
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Look at java.util.* for some good examples of the use of both.

Difference between Abstarct Class and Interface

HI,
Here is a simple one for the gurus but quite important for me.
What is the difference b/w an Interface and an abstract class?
Why do we need each one of them?
I would appreciate if you people can give examples of each so that I amy understand fully
Thanks in advance...

A normal class (not abstract) has a special behaviour, like java.awt.Frame. A Frame is a frame no matter how you subclass it. If you create a subclass it will still be able to be displayed by calling it's show method. So by using a normal class you can create a type of class.
An abstract class does the same, but it leaves some of the code unwritten. For instance java.lang.Number. This class is abstract becuase it has no knowledge of how to store the number in memory. But it knows that it is a number, and any subclass will still be a number. You could create a subclass of Number that can hold the time in milliseconds and checks your system clock to see what the time is, it could also have methods that return the time in another country, but it would still be just a Number.
An interface is a way to describe what an object can do, not what it is. So with java.lang.Comparable as an example you can make any class comparable. This means that no matter what type of object you have, it can be compared with other objects. So you can have a subclass of Frame that can be compared with other windows. Or a subclass of Number that can be compared with other Numbers. You can even compare those two different types if you like. So you could compare a window with a number.
That is the difference between abstract classes and interfaces.
I hope you could follow my arguments, it isn't an easy subject,
Daniel

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Hello, all!
I am studying javaFX in general. As far as I understand there is no main difference between java applet and javafx, except javafx has different syntax and library simple to use. Is it right?

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What's the difference between Java SDK and the Enterprise Edition? Are they both free?

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Difference between Data Class and Delivery Class

What is the Difference between Data Class and Delivery Class , what happens Phisically to the Data .
Moderator message: what is the difference between your question and a question that we'd welcome here in the forums?
[Rules of engagement|http://wiki.sdn.sap.com/wiki/display/HOME/RulesofEngagement]
Edited by: Thomas Zloch on Nov 22, 2010 1:17 PM

What is the Difference between Data Class and Delivery Class , what happens Phisically to the Data .
Moderator message: what is the difference between your question and a question that we'd welcome here in the forums?
[Rules of engagement|http://wiki.sdn.sap.com/wiki/display/HOME/RulesofEngagement]
Edited by: Thomas Zloch on Nov 22, 2010 1:17 PM

Difference between abstract classes and interfaces

I actually wonder about what are the differences between abstract classes and interfaces may somebody give an example code about it?
and i have one more question how can i use interfaces like multiple inheritance ? i mean when i implement an interface like
class a extends b implements c,di have to use all c and d methods but what that methods means?
I mean as i know we cannot make implementations of methods in interfaces
but for example in runnable interface there is a method like run() and it has been defined somewhere because it knows what to do(i mean when it will run), i just write my code into that method .

Once you get past the starting point (I am referring to the OP here), there are a few salient differences:
You can only extend (or generalize) a single superclass; however, you can implement (or realize) multiple interfaces. As such, all things being equal, using an interface in lieu of an abstract class 'frees' your design. Later, if you want the implementor of an interface to inherit from another class, there is not issue.
Any abstract method specifies a contract. However, abstract classes allow you to also add common behavior to subclasses. This is an overused justification for abstract classes, IMO. You can achieve the same effect using delegation and still having interfaces.
Always program to interfaces wherever possible. This means that you define an interface and have an implementing class (usually at a minimum). Do not do this for all your classes, but rather the ones that make your system unique (the domain model or M in MVC architecture). This allows you to later change implementation with a minimal amount of refactoring. This is a core precept from the Group of Four and any number of decent programming books.Best of luck.
- Saish

Difference between Material Class and Batch Class

Hi!
What is the difference between Material Class and Batch Class?
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[svn] 4112: Further work for FXG to SWF transcoding - checking in some work resulting from collaborating with Kaushal to correct FXG transforms and gradient transforms as well as cater for differences between Java AffineTransform and the SWF Matrix type .

Revision: 4112
Author: [email protected]
Date: 2008-11-14 10:05:42 -0800 (Fri, 14 Nov 2008)
Log Message:
Further work for FXG to SWF transcoding - checking in some work resulting from collaborating with Kaushal to correct FXG transforms and gradient transforms as well as cater for differences between Java AffineTransform and the SWF Matrix type.
QE: Not yet.
Doc: No
Checkintests: Pass
Reviewer: Kaushal
Modified Paths:
flex/sdk/trunk/modules/swfutils/src/java/flash/fxg/dom/GraphicContentNode.java
flex/sdk/trunk/modules/swfutils/src/java/flash/fxg/dom/fills/LinearGradientFillNode.java
flex/sdk/trunk/modules/swfutils/src/java/flash/fxg/dom/fills/RadialGradientFillNode.java
flex/sdk/trunk/modules/swfutils/src/java/flash/fxg/dom/strokes/LinearGradientStrokeNode.j ava
flex/sdk/trunk/modules/swfutils/src/java/flash/fxg/dom/strokes/RadialGradientStrokeNode.j ava
flex/sdk/trunk/modules/swfutils/src/java/flash/fxg/swf/AbstractFXGGraphics.java
flex/sdk/trunk/modules/swfutils/src/java/flash/fxg/swf/TypeHelper.java
Added Paths:
flex/sdk/trunk/modules/swfutils/src/java/flash/fxg/dom/ScalableGradientNode.java

Question about main difference between Java bean and Java class in JSP

Hi All,
I am new to Java Bean and wonder what is the main difference to use a Bean or an Object in the jsp. I have search on the forum and find some post also asking the question but still answer my doubt. Indeed, what is the real advantage of using bean in jsp.
Let me give an example to illustrate my question:
<code>
<%@ page errorPage="errorpage.jsp" %>
<%@ page import="ShoppingCart" %>

<jsp:useBean id="cart" scope="session" class="ShoppingCart" />
<html>
<head><title>Shopping Cart</title></head>
<body bgcolor="#FFFFFF">
Your cart's ID is: <%=cart.getId()%>.
</body>
<html>
</code>
In the above code, I can also create a object of ShoppingCart by new operator then get the id at the following way.
<code>
<%
ShoppingCart cart = new ShoppingCart();
out.println(cart.getId());
%>
</code>
Now my question is what is the difference between the two method? As in my mind, a normal class can also have it setter and getter methods for its properties. But someone may say that, there is a scope="session", which can be declared in an normal object. It may be a point but it can be easily solved but putting the object in session by "session.setAttribute("cart", cart)".
I have been searching on this issue on the internet for a long time and most of them just say someting like "persistance of state", "bean follow some conventions of naming", "bean must implement ser" and so on. All of above can be solved by other means, for example, a normal class can also follow the convention. I am really get confused with it, and really want to know what is the main point(s) of using the java bean.
Any help will be highly apprecaited. Thanks!!!
Best Regards,
Alex

Hi All,
I am new to Java Bean and wonder what is the main
difference to use a Bean or an Object in the jsp. The first thing to realize is that JavaBeans are just Plain Old Java Objects (POJOs) that follow a specific set of semantics (get/set methods, etc...). So what is the difference between a Bean and an Object? Nothing.
<jsp:useBean id="cart" scope="session" class="ShoppingCart" />
In the above code, I can also create a object of
ShoppingCart by new operator then get the id at the
following way.
ShoppingCart cart = new ShoppingCart();
out.println(cart.getId());
...Sure you could. And if the Cart was in a package (it has to be) you also need to put an import statement in. Oh, and to make sure the object is accessable in the same scope, you have to put it into the PageContext scope. And to totally equal, you first check to see if that object already exists in scope. So to get the equivalant of this:
<jsp:useBean id="cart" class="my.pack.ShoppingCart"/>Then your scriptlet looks like this:
<%@ page import="my.pack.ShoppingCart %>
<%
ShoppingCart cart = pageContext.getAttribute("cart");
if (cart == null) {
    cart = new ShoppingCart();
    pageContext.setAttribute("cart", cart);
%>So it is a lot more work.
As in my mind, a normal class can also
have it setter and getter methods for its properties.True ... See below.
But someone may say that, there is a scope="session",
which can be declared in an normal object.As long as the object is serializeable, yes.
It may be
a point but it can be easily solved but putting the
object in session by "session.setAttribute("cart",
cart)".Possible, but if the object isn't serializable it can be unsafe. As the point I mentioned above, the useBean tag allows you to check if the bean exists already, and use that, or make a new one if it does not yet exist in one line. A lot easier than the code you need to use otherwise.
I have been searching on this issue on the internet
for a long time and most of them just say someting
like "persistance of state", "bean follow some
conventions of naming", "bean must implement ser" and
so on. Right, that would go along the lines of the definition of what a JavaBean is.
All of above can be solved by other means, for
example, a normal class can also follow the
convention. And if it does - then it is a JavaBean! A JavaBean is any Object whose class definition would include all of the following:
1) A public, no-argument constructor
2) Implements Serializeable
3) Properties are revealed through public mutator methods (void return type, start with 'set' have a single Object parameter list) and public accessor methods (Object return type, void parameter list, begin with 'get').
4) Contain any necessary event handling methods. Depending on the purpose of the bean, you may include event handlers for when the properties change.
I am really get confused with it, and
really want to know what is the main point(s) of
using the java bean.JavaBeans are normal objects that follow these conventions. Because they do, then you can access them through simplified means. For example, One way of having an object in session that contains data I want to print our might be:
<%@ page import="my.pack.ShoppingCart %>
<%
ShoppingCart cart = session.getAttribute("cart");
if (cart == null) {
    cart = new ShoppingCart();
    session.setAttribute("cart", cart);
%>Then later where I want to print a total:
<% out.print(cart.getTotal() %>Or, if the cart is a JavaBean I could do this:
<jsp:useBean id="cart" class="my.pack.ShoppingCart" scope="session"/>
Then later on:
<jsp:getProperty name="cart" property="total"/>
Or perhaps I want to set some properties on the object that I get off of the URL's parameter group. I could do this:
<%
ShoppingCart cart = session.getAttribute("cart");
if (cart == null) {
    cart = new ShoppingCart();
    cart.setCreditCard(request.getParameter("creditCard"));
    cart.setFirstName(request.getParameter("firstName"));
    cart.setLastName(request.getParameter("lastName"));
    cart.setBillingAddress1(request.getParameter("billingAddress1"));
    cart.setBillingAddress2(request.getParameter("billingAddress2"));
    cart.setZipCode(request.getParameter("zipCode"));
    cart.setRegion(request.getParameter("region"));
    cart.setCountry(request.getParameter("country"));
    pageContext.setAttribute("cart", cart);
    session.setAttribute("cart", cart);
}Or you could use:
<jsp:useBean id="cart" class="my.pack.ShoppingCart" scope="session">
<jsp:setProperty name="cart" property="*"/>
</jsp:useBean>The second seems easier to me.
It also allows you to use your objects in more varied cases - for example, JSTL (the standard tag libraries) and EL (expression language) only work with JavaBeans (objects that follow the JavaBeans conventions) because they expect objects to have the no-arg constuctor, and properties accessed/changed via getXXX and setXXX methods.
>
Any help will be highly apprecaited. Thanks!!!
Best Regards,
Alex

Is there any difference between java Beans and general class library?

Hello,
I know a Java Bean is just a java object. But also a general class instance is also a java object. So can you tell me difference between a java bean and a general class instance? Or are the two just the same?
I assume a certain class is ("abc.class")
Second question is is it correct that we must only use the tag <jsp:useBean id="obj" class="abc.class" scope="page" /> when we are writng jsp program which engage in using a class?Any other way to use a class( create object)? such as use the java keyword "new" inside jsp program?
JohnWen604
19-July-2005

a bean is a Java class, but a Java class does not have to be a bean. In other words a bean in a specific Java class and has rules that have to be followed before you have a bean--like a no argument constructor. There are many other features of beans that you may implement if you so choose, but read over the bean tutorial and you'll see, there is a lot to a bean that is just not there for many of the Java classes.
Second question: I'll defer to someone else, I do way to little JSP's to be able to say "must only[\b]".

Differences between Java Servlet and Portlets

Hello,
May anyone let me know the differences between Java Servlet, JavaBeans and Portlets? It seems quite similar to each other... By the way, what are differences between a servlet container and portlet container? Thank you.
Charoite

JavaBeans are totally different from servlets or portlets. JavaBeans can be used in just about any environment. A JavaBean is basically a java class with a no-arg constructor which follows certain naming conventions for its get and set methods.
Servlets can only function in an "web containers" which are provided by application servers which support servlets. The main function of servlets is to process requests (usually http requests) and generate output (usually web pages). They usually perform validation and other processing and then delegate the web page generation to a jsp.
Portlets are similar to servlets but rather than generating an entire web page, their output is relegated to a portion of a page. A single web page may contain the output of several portlets. These portlets can communicate with each other. The portlet container provides the functionality to merge the output of the various portlets and the infastructure required to support the portlets.

Difference between static class and singleton?

Hi I wonder what could be the difference between static methods and singleton?
In singleton at any point of time there will be only one object existing in the JVM. We create singleton to avoid multiple object creation for that class.
If I make all the methods in the class as static also it does the same job. The memory will be allocated once. Even there wont be any object in this case, so time required for object creation also can be saved. looks like more efficient but still why need singleton?
This question is also posted in java programming forum. The thread is as follows:-
[Click on this to visit that thread |http://forum.java.sun.com/thread.jspa?threadID=5278517&tstart=0]
Edited by: murrayb9654 on Mar 25, 2008 8:20 AM

yawmark wrote:
Static class is a realization of singleton pattern.Not in any conventional sense.
~Especially since a static class is completely different from a class with all static methods.

Difference between Java class and JavaBean?

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