From my point of view, unless you have a prodigious mind, you need to use several times a function to remember it... and there is a lot oof objects an functions out there. So the best approach is to think if an object could have a function related to it that could be handy and search for it.
However, sometimes if best try to think out of the box and try your best shoot and then see if there is that function out there.

As I can understand you can just find those methods in the installed Java editors like IJ IDEA. They come handy when you need to find the specific methods of classes. Just typing, for instance, "str." it will show you every single method that class "str" has. Actually, in my opinion, it is the best way to practice. However, not all editors may provide the methods of classes. Sublime, of course is one of them. The only reason to use Sublime and such editors is that they are super fast.

You should always try to find methods, with out withour Google. Is the way to learn!