Executing JavaScript on the JVM

As you will see in subsequent sections, navigating and manipulating the JVM’s class and object structure can result in verbose and cumbersome Python code. Therefore, Javabridge ships with the JavaScript interpreter Rhino, which runs on the JVM. In many cases, the most convienient way to interact with the JVM is to execute a piece of JavaScript.

For more information on using Rhino with the JVM see https://developer.mozilla.org/en-US/docs/Rhino/Scripting_Java

Examples:

>>> javabridge.run_script("2 + 2")
4

>>> javabridge.run_script("a + b", bindings_in={"a": 2, "b": 3})
5

>>> outputs = {"result": None}
>>> javabridge.run_script("var result = 2 + 2;", bindings_out=outputs)
>>> outputs["result"]
4

>>> javabridge.run_script("java.lang.Math.abs(v)", bindings_in=dict(v=-1.5))
1.5

A conversion is necessary when converting from Python primitives and objects to Java and JavaScript primitives and objects. Python primitives are boxed into Java objects - Javascript will automatically unbox them when calling a method that takes primitive arguments (e.g. the call to Math.abs(double) as in the above example. The following is a table of bidirectional translations from Python to Java / Javascript and vice-versa:

Python	Java - boxed	Java-primitive
bool	java.lang.Boolean	boolean
int	java.lang.Integer	int
long	java.lang.Long	long
float	java.lang.Double	double
unicode	java.lang.String	N/A
str (Python->java only)	java.lang.String	N/A
None	null	N/A