How to search for text in a whole Eclipse project instead of file by file

You can navigate to

Search >> File

When in you can then specify your string and a working set. Set the working set to your project folder. Depending on how picky you want to be you can set the file name patterns too. I have not tried but I am assuming you can do *.* to search everything under the sun.

You can use the below image as a reference (I used Eclipse - Galileo). I searched for the string "System" and got results for my class file and my interface file. Once you search all occurances will show up in a search tab (normally docked on the bottom of the screen).

Each instance can be double-clicked to take you to that specific occurance.

You can also use the Ctrl+H shortcut to search files in Eclipse project.