How to use javabean

Question

can anyone can have a easy understand explain for how to use javabean?
for example, if i am going to have a bean named "Dog", which will can speak "blah blah blah". what is the procedure to get it work?
thanks

Answer 1

Hi.
I'm not quite sure what you're asking, but I'll give it a shot at a simple explanation. Let's say you create a Dog bean. A Bean is really just a Class that follows some general rules and naming conventions to make interpreting of the exported interface easier.
The Java Beans specification says that the Dog bean should be serializable - That is, you can modify the values in the fields of Dog (i.e., you could change it's breed, or it's name, or it's owner, or what ever other fields you have), and write it out to a file, and load it back at a later time, and these fields would still have memory of the changes you made earlier. This is called persistance.
Further to this, a bean declares properties as fields xxx that have matching methods getXxx and setXxx. Let's say you wish to have several dogs, one that speaks "arf", one that says "ruff", another that says "woof", one that says "yip yip, one that says "bow wow", and finally, one that says "yo quiero Taco Bell". Then, you would have a property called word that would be defined in the following way:
private String word;
public void setWord(String word) { this.word = word; }
public String getWord() { return word; }Then, using your favourite Bean box or design tool, you would create several dogs, and set the word differently for each one.
The code for speak would be this:
public void speak() { System.out.println(word); }The benifit provided using the beans conventions of getXxx and setXxx allows the Bean Box to determine that there is a property called word, and that you can set this property to allow you to change the word that is spoken without overwriting the speak method.
I'll say this again, becuase this is important: Anything that can be done with beans can be done without. The advantage to using beans is that a tool like a bean box, or the Introspector class, can dynamically determine which fields provided by a class are intended for use by another external class, AND which methods are used to set or retrieve the values of those fields.
For example, you could define the same property with the following code:
public String word;
public void changeToNewWord(String word) { this.word = word; }
public String whatDoesItSay() { return word; }The problem with this code, however, is that an introspector or bean box would have ABSOLUTELY NO IDEA that the changeToNewWord method is the method that should be called to set the property word.
That's the basic idea. It goes much further than this, as you can then define events, such as the SawAnotherDogEvent that cause the bean to call the method speak. Also, you could create a custom bean info class that would tell the introspector that the changeToNewWord method was the setter method for word. The whole point is to provide extra information about you're class so that it can be recognized by some other coding as certain types of fields.
To find out more, there is an excellent tutorial for Beans on the java developer website (java.sun.com), and the Beans specification is also there. Hope this helps you out. Good Luck!