What Exactly Is a JavaBean?

A JavaBean is just a standard:

1. All properties are private (use getters/setters).
2. A public no-argument constructor.
3. Implements Serializable.

That’s it. It’s just a convention — but lots of libraries depend on it.

With respect to Serializable, from the API documentation:

Serializability of a class is enabled by the class implementing the java.io.Serializable interface. Classes that do not implement this interface will not have any of their state serialized or deserialized. All subtypes of a serializable class are themselves serializable. The serialization interface has no methods or fields and serves only to identify the semantics of being serializable.

In other words, serializable objects can be written to streams, and hence to files, object databases — anything, really.

Also, there is no syntactic difference between a JavaBean and any other class: a class is a JavaBean if it follows the standard.

There is a term for it because the standard allows libraries to programmatically do things with class instances you define in a predefined way. For example, if a library wants to stream any object you pass into it, it knows it can, because your object is serializable (assuming the library requires your objects to be proper JavaBeans).

Source (Stack Overflow)