Ask HN: What is a good phone for to write code on?

None. Even tablets are considerably less than optimal (believe me, I've been trying for years now). Nothing on iOS has been suitable (caveat: I have not tried in the last six months), Android offerings tend to be better.

Java is even worse than some of the other options because of the syntactic noise: too many special characters are required in too many places.

At best you could do some limited code generation if you used some GUI-oriented block mechanism (e.g., Blockly that outputs Java code), but phone displays are small even for that limited form of interaction.

I recommend getting a low-end laptop. No phones (or tablets) are good for writing code. Bonus: The laptop will probably be cheaper, too.

another thing came to mind today

the samsung galaxy note 8 plugged into the hp elite x3 lapdock is a great candidate. doing this gives you a larger screen, keyboard, and trackpad.

If you can make Coda fit into your workflow, that plus a Bluetooth keyboard can be nice. Other than that, the on screen keyboard will be awful. Find a phone with a real keyboard (which seriously limits your options).

How about a Windows tablet?

A tablet by any manufacturer would be great.

Gemini PDA is my recommendation.