cmd+shift+o (cmd+shift+n in older versions) leads to the file open dialog (on mac).
You can use * chars as wildcards. If there is more than 1 file with the name, you will see the directory of the file for each entry to help you make the choice.
Just hit quickly Shift Shift in a row to reveal a pop-up window to search for everything. You can then start typing to search for files. It's a fuzzy finder, so to match e.g. SomeClassWithALongName.java you can just type: sclwlna (or other letters combination, which has the same order of occurance in the target file name).