In this tutorial I will show you how to make Eclipse display line numbers next to your code.
To enable line numbers to the left of your code go to Window at the top and then select Preferences. Next click on the little arrow to the left of General and after that the one next to Editors. Finally click on the Text Editors option and check the Show line numbers option right here.
For a more detailed explanation and much more, check out my book Sams Teach Yourself Mod Development for Minecraft in 24 Hours.