I am trying to convert old B4A code to Java so that I can rebuild the UI slightly faster than starting from scratch. My idea is to compile the code into java and just go from there. Is this realistic? I have been trying to do this but keep getting compiler errors regarding the device that the UI turns on. Am I wasting my time? I am doing this because I have substantially more experience with Java than B4A.
No.
B4A is designed to use the B4X Ide.
I don´t think it makes much sense to use the code generated to further develop with java.
I suggest to get familar with B4X Language and use your java knowledge to implement something with java using inline java in B4A or wrapping a library to use them in B4A. You java-knowledge will help here much.