[lanna]

You just made TWO typos: "display-name" vs "display_name" and "_name" vs "name", automatically counter-argumenting your point.

It is also for documentation. With the declared constants, we know all possible values. With plain strings, how am I supposed to know which values to use?

The benefits far outweigh the marginal cost.

[ramsicandra]

The -, _, and leading _ are just variations of white space / separator I have encountered. I think it's possible to document all the allowable values in the Javadoc section of the function that takes in string as their argument.

In the specific android example, I would put it here. Under projection params where it takes in all the Images.Media.* string consts.

https://developer.android.com/reference/android/content/Cont...

Though, if it's a practice of Java Engineer to document allowable enum like string as a constant, then I can say that's a valid argument.