.jar files are just specially packaged .zip files for distributing Java programs and libraries. .class files are Java bytecode. What source code files are you

.jar files are just specially packaged .zip files for distributing Java programs and libraries. .class files are Java bytecode. What source code files are you seeing? What are the filenames, etc.? JetBrains's IDE source code would likely be Kotlin (.kt, .kts file extension) or Java (.java file extension) source code files.