CONVENTIONS!!!!!!!!!!!!!!!!!!!!!!!!!
They are very important!!!!!! It's setting a standard in a programming language, imagine working in a group and you were naming all of your objects in capitalized letters or using underscores instead of camel casing would make it very confusing for others. If you decide to modify the standard java conventions make sure you document it for others working within your team, remember communication is key.
Let me explain this myself
Let's say i made a home location
Code:
public static final Location HOME_LOCATION = Location.create(23, 50);
that's a constant, now you may change that WHILE YOUR PROGRAM IS NOT RUNNING you may change those values manually and recompile your program, BUT when my program is running I CANNOT CALL
Code:
HOME_LOCATION = Location.create(10,0);
JAVA WILL NOT LET ME, this is a constant it's expected to stay that way as long as the program is running.
Mutable classes can have its internal variables changed while the program is running so having their coordinate values should be mutable and that's completely fine since it's a variable that's expected to change
Immutable classes are not supposed to have its internal variables change, it's purpose is to be created once and it stays that way! so you can only have getters for that, a good example would be creating the size of a model on a man NPC, that should stay as is once that NPC has been created or a player id. There are many examples for this, i suggest searching some information on stack overflow, they have great examples