How to collapse blocks of code in Eclipse?

Preferences -> C++ -> Editor -> Folding ?

Make a right click in the editor window and go to preferences there, then only the editor-relevant section of the preferences dialog will appear. This works for JDT, CDT etc...

Try this option: Preferences > Java > Editor > Folding > Enable folding

You can do ( Ctrl + Numpad_Divide ) to enable folding.
Also if you Right Click on the area where the + or - was supposed to be, you can see there is a folding option.