BeanShell is a small, free, embeddable, Java source interpreter with
object scripting language features, written in Java. BeanShell executes
standard Java statements and expressions, in addition to obvious
scripting commands and syntax. BeanShell supports scripted objects as
simple method closures like those in Perl and JavaScript(tm). You can
use BeanShell interactively for Java experimentation and debugging or
as a simple scripting engine for your applications. In short: BeanShell
is a dynamically interpreted Java, plus some useful stuff. Another way
to describe it is to say that in many ways BeanShell is to Java as
Tcl/Tk is to C: BeanShell is embeddable - You can call BeanShell from
your Java applications to execute Java code dynamically at run-time or
to provide scripting extensibility for your applications.
Alternatively, you can call your Java applications and objects from
BeanShell; working with Java objects and APIs dynamically. Since
BeanShell is written in Java and runs in the same space as your
application, you can freely pass references to "real live" objects into
scripts and return them as results.

With version 2.0 BeanShell becomes a fully Java compatible scripting
language. BeanShell is now capable of interpreting ordinary Java source
and loading .java source files from the class path. BeanShell scripted
classes are fully typed and appear to outside Java code and via
reflective inspection as ordinary classes. However their implementation
is fully dynamic and they may include arbitrary BeanShell scripts in
their bodies, methods, and constructors. Users may now freely mix
loose, unstructured BeanShell scripts, method closures, and full
scripted classes.