Yes, you are right with your assumption. After changing the code, you have to recompile the project, so that the changes come into effect.
Eclipse as IDE has the comfortable functionality to rebuild the project automatically after each change. This function is enabled after installation, you can check it in the menu at “Project” -> “Build Automatically”. Furthermore, you can use “Project” -> “Build All” to manually compile the project or use the ant build scripts.
After this building step (automatically or manually), all your changes should be visible in the simulations.