Calpoly: http://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html
Cambridge: https://www.cl.cam.ac.uk/teaching/0809/LongVac/problems.pdf
CyberComSweden: https://github.com/cybercomsweden/javaee-exercises
ImageJ: https://imagej.net/Debugging_Exercises#Exercise_1:_Stack_Traces_and_Breakpoints