It is many small java-projects in one directory. I did this work on the basis of the spezialist java courses levels 1 and 2.
I repeated java-syntax, collections and sorting, files and streams, threads, databases connection and sql-cueries. I learned a couple of patterns, swing and javaFX. Swing and javaFX are also located in separate repositories: swing_write_read, swing_box, java_fx, java_network.