Why are filenames in Java the same as the public class name? [closed]

Answer 1

As long as it is not public a class can have a name different from its file name. The class can also have main method. Class file will be generated with the class name but not with the source file name. The class name should be used to execute it.

Reason is: default class is package private, thus javac doesn't have to find this source file of this to compiler some other java program from outside of package.

Answer 2

It is useful in locating the class. i.e. Suppose different file names are allowed and if you have created an instance of a class then the compiler has to search the class in all file instead if the file-names are same as that of the class the performance of locating and using the class is increased. Their might be other reasons too.

Answer 3

Each public class must be in a file where the FileName matches the ClassName and a package where the Packagename represents the Directory structure, written in the dotted-form (slashes become dots, like com/example/app becomes com.example.app).

This convention is not random. The compiler has to be able to find the source files and the class loader has to be able to find the implementation. Matching package names and classnames makes this really simple and, more important, fast.

This convention does not apply to non-public classes. This is because non-public classes have a very limited visibility and can only be used within the package where they are defined. Thus, in both cases, the compiler and the runtime environment have already located the correct files.

Answer 4

To be more specific, the filename should have the same name as the public class name in that file, which is the way to tell the JVM that this is what the entry point is for you.

Answer 5

I was about to say, that it is simply a must. But I looked at the JLS, and it is not that strict. From the JLS's perspective, it is left to the compiler to choose whether to set such a restriction or not.

Practically spoken - common compilers do have that restriction, and, as other already explained, it's much easier for the compiler to find a compilation unit or for a classloader to find a class file with such a restriction in place.

Answer 6

It is just the convention set by Sun, the makers of Java.
The purpose is organization; the reason is so that everyone who codes in Java will have a consistant way of naming files.