Why does my mouse cursor change to a plus sign in Eclipse?
Simply do the below steps -
Window -> Close All Perspectives. And, rebuild your perspective.
Window -> Open perspective -> Java(Default) -> Ok.
Hope these 2 steps may helpful to you.
You might have selected the tool, `Toggle Block Selection Mode Alt+Shift+A so that's why your mouse point is converted to + sign, Toggle it off and it will be simple again.
More to read about this Mode: Click Here