And if it is necessary, should I set every class to private until I find that it needs public access?
At the actual class level, such as
public class HelloWorld {...} , you'll be safer defaulting to public. If it's private, even the public main methods won't be available to the
Java runtime, which will cause you endless headaches as you wonder why the simplest pieces of code don't want to work.
So, what can be public? Classes, methods and instance variables can have access modifiers placed upon them.
For the most part, the vast majority of classes you create will be public.
The vast majority of instance variables you declare will be private. Data is important, and you don't want everyone to have direct, unimpeded access to your data.
Methods that work internally on data, and aren't used by clients, but are really part of the internal working of the class should be private. If other components need to call a particular method, you need to make it public.
It's always a balancing act, that's for sure. Initially, I think seeing four access levels seems overwhelming, but the more you program, the more you'll see cases where the use of protected or default access is not only smart and clever, but it's also elegant. I remember seeing the Factory
pattern implemented propertly for the first time, and I thought "wow, that really makes sense."
Plus, a Java class file can only have one public class in it. I sometimes like to add comparator classes to a Java file where only classes in that Java file really needs to call the class implementing the comparator interface. Since only one class in a single Java file can be public, these second and third classes must have either a package or protected access modifier.
It'll grow on you. Give it a chance.
-Cameron McKenzie
