The Wolfram Language's J/Link system provides a uniquely seamless interface to the Java environment. With J/Link you can immediately access Java classes and objects from within the Wolfram Language without any Java programming. J/Link also provides a complete library for calling the Wolfram Language from within Java programs.
Calling Java from the Wolfram Language »
LoadJavaClass — load and set up a Java class for use from the Wolfram Language
JavaNew — create a Java object
JavaObject ▪ JavaBlock ▪ ...
Calling the Wolfram Language from Java »
KernelLink ▪ MathLink ▪ Expr ▪ MathGraphicsJPanel ▪ ...