Multiple classes in the same source file

Question

I'm not sure what this is called, having multiple classes in the same source file. At first I thought it ws called subclassing but then I googled it and found that subclasses are just derived classes. Here's an example of what I'm talking about.
public class A {
class B {
class C {
}So first of all, what is having multiple classes in the same source file called?
Secondly, what are the advantages/disadvantages of this?
Thirdly, can you have a class completely WITHIN a class (same source file but inside the class not outside) and what are the advantages/disadvantages of this?

Answer 1

Advantage: You can reduce the number of source files specialy when your secondry classes are used only in the public class of the file.
Disadvantage: Normaly it make things more clear if we have one-to-one correspondance of class and source files. This make things easy when you want to find the java file of a perticuler class file. Also If you later wanted to create a seperate public class with a same name as one of those secondry classes you got lots of changes to do.
You can avoid this by creating them as nested classes
ex:-
public class MyPublicClass{
   private static class MyInnerClass{
}this way the inner class will create a class file with name "MyPublicClass$MyInnerClass.class" instead of just "MyInnerClass.class"
And also if you declare the inner class as public you can access them from out side