Shortcut key for switching from projects windows to source file

Here is my work flow

Suppose I have two files open A.java and B.java. Say I am editing A.java and it is in focus. I press Alt+1 to switch to "Projects window", and browse the project work-space.  Then I want to refocus on A.java.

When I press Ctrl+Tab, B.java is selected. In order to select A.java I have to Ctrl+Tab and then Shift+Tab while holding the Ctrl button. Is there a single shortcut key to focus on A.java without closing the Projects window?