What are JavaBeans in plain English?

 

Before I start I would just like everyone know that I did indeed spend a good time googling this and found a lot of explanations and definitions. But even so after spending hours reading the subject still seems rather vague. I know I have to ask questions that can better the community but this one is just for me to see if I have a clear understanding of JavaBeans.

From what I can make out, a JavaBean is basically a class just like any other java class except that it adheres to certain conventions, ie:

  • The class must implement Serializeable
  • Class properties are assumed to be private and their names start with a lowercase letter
  • Each property must have it's respective getter and setter methods.
  • Each setter method starts with the prefix 'get' followed by the property name eg setName()
  • Setter methods are public and void
  • Same applies to the getter methods (prefix 'get', public, return type respective property class type etc.)
  • For boolean properties instead of 'get' one uses the prefix 'is'
  • Strictly speaking it is the instance of the class that is considered a 'bean' not the class itself.

    • And there you have it, after a very long time of reading, that's what I can make out... Is that it? Am I close? Do I have this completely wrong?

    ...Thanks for everyone's answers so that I could update this bullet list :-)

    A javabean is a standard . All Javabeans have the following 3 qualities:

    1) The class implements Serializable
    2) All fields have public setters and getters to control access.
    3) A public no-argument constructor.

    Yep, that's pretty much it.

    Just a couple of extra bits:

  • Getters take no parameters, and setters take a single parameter of the same type as the property
  • Properties can be read- or write-only by omitting the setter or getter respectively
  • boolean getters use the prefix 'is'

    • And I think strictly it's the instances that are "beans", not the class.

    Is that it? Am I close?

    Yes, you are relatively correct. Most beans adhere to such basic rules for definition. However, just a few more things to add. To distinguish beans from POJO (Plain Old Java Object), beans have a default constructor and usually implement the serializable interface.

    This allows you to work with basic models across many frameworks. Beans are mostly used for storing and retrieving data in a simple layout structure so data models can be shared throughout specific architectures. Examples include firing events in a UI using the same data for working with different dialogs and or retrieving results for a given ORM (Object Relationship Mappings). Additional examples you may want to look at are DTO (Data Transfer Object), VO (Value Objects), and EJBs (Enterprise Java Beans).

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