BlueJ at Home

FAQ: Problems using BlueJ at home

It is generally not possible for us to help solve problems with using BlueJ on your laptop or home computer because there are so many different things that can go wrong, and it is almost impossible to diagnose them without actually seeing the computer. However, here are some generally useful comments.

  • Make sure you have followed all the instructions on the Working at Home page.
  • Make sure your folder settings (or finder settings) make file extensions visible. (In Windows 7, in a folder window (Windows Explorer), Organize menu -> Folder and Search Options -> View tab: ensure that "Hide extensions for known file types" is OFF)
  • Make sure that you have the right version of Java: you should have version 1.8, and you must have the JDK, not the JRE. (The JDK has the compiler, which you need for writing your own Java programs; the JRE just lets you run Java programs written by someone else.)
  • In BlueJ, check that the ecs100.jar file is installed: Tools menu -> Preferences -> Libraries tab, should list the User Libraries. The location of the ecs100.jar file should be listed in the pane at the bottom. If it isn't there, then you didn't put it in the right place. The text above the bottom pane should be showing the folder that ecs100.jar should be in.
  • BlueJ Frequently Asked Questions