The Applet API was deprecated for removal in Java 17, and will most likely be removed completely in Java 25. There are classes within OpenMap that utilize these APIs either directly or indirectly. Specifically, the Environment class imports and uses both java.applet.Applet and javax.swing.JApplet, which would cause an initialization error. Of course, the OpenMapApplet class utilizes the API, but would only be utilized in environments where a browser that supports the Java plugin exists.

Edit: Officially targeted for removal in Java 26