I think the trick is to take a problem and "see" the higher-level patterns in the solution rather than the specifics.
Not remembering what you can look up is the beginner's shortcut, not looking up what you can just remember is the advanced tactic, and is what gets you to fluency in any subject.
In reality, the things you tend to google every time you need it are precisely things you don't actually use enough to memorize. When you do memorize them, enough time elapses each time to where you forget.
My take is that there is value in putting in deliberate effort to remember the key takeaways from our readings or talks we've listened to (among other things), as the original comment pointed out. The blog post is then on how to go about doing it.
As you continue programming in a given language, you automatically memorize low-level things like syntax and idioms. That's not something that everyone needs or wants to practice explicitly with flashcards or whatever (that's not how I learn, anyway). But memorization of syntax is absolutely critical to achieve "fluency" in the programming language, just as in human language.
Imagine a monolingual English speaker learning German and scoffing at their classmates' attempts to internalize the grammar rules. You can Google or look all that stuff up in a few seconds! But having to pause and look up every conjugation or word ordering is exactly what prevents the learner from actually communicating clear ideas at a useful speed in their target language.
Java is especially good for that, though. You just add a point to a variable and choose what you want (out of 1000 methods).
I thought so too. Then I ended up with having to write a lot of tSQL. And even though I used them quite regularly, I always had to look up the syntax for things like MERGE, or PIVOT. So I made flashcards, and it has increased my productivity enormously. Not so much because looking up the syntaxes took particular much time, but it always interrupted my train of thoughts. And before I know the syntax by heart I always felt this slight resistance to use these constructs because I knew I had to look them up and would probably make some small mistake somewhere et c.