Indeed - most Java IDEs have FernFlower built in, so it’s dead easy.

Decompiled Java is surprisingly close to the original, especially compared to eg. decompiled C++; good luck with that. You get all the class, function and variable names back on the original line numbers.

What you do not get back is any comments. So you can see what and how, but not why. Admittedly, most comments are kind of useless and do not explain ‘why’ very well, but for weird-but-critical code they can be essential.