I really like Processing. Processing is a Visual Programming language, and it is based on Java. It is designed to run either as an Applet, a Standalone App, or as a Java Component; running a Processing Sketch as a Component is the one with less documentation, but probably one of the most interesting and powerful applications of it.
This is a small guide on setting up a Processing Sketch as a Java component, ready to use on your Swing or AWT desktop applications.

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