This functionality is provided by the Code Recommenders
plugin. It comes with the Eclipse Luna for Java SE, but for some reason it is not bundled in the EE version. Of course you can install it manually from the eclipse marketplace.
To activate it go to Window -> Preferences -> Code Recommenders -> Completions -> Check enable intelligent code completion. You can also select in which type of completions you are interested in. The exact feature you are looking for is called "Subwords completion processor" (and I cannot live without it :D)
