IntelliJ IDEA 13.1.0 Web Help

This helpful feature analyses your text in the visible scope and suggests to complete a word with a keyword, class name, method or variable. So doing, the prototype is highlighted in the source code.

To expand a string at caret to an existing word
  1. Type the initial string.
  2. Press . The editor shows the first suggested value.
  3. Press to accept the suggested word, or continue pressing until the desired word is found.