In Java, can we divide a class into multiple files

Question

Any possibility to divide a class into multiple physical files using Java?

Answer 1

No, the whole of a class has to be in a single file in Java.

If you're thinking of C#'s "partial types" feature, there's no equivalent in Java. (If you weren't thinking of C#, ignore this :)

Answer 2

Yes You Can!

For the sake of completion:

Since Java 8, you have the concept of default methods.

you can split up your class into multiple files/subclasses by gently abusing interfaces

observe:

MyClassPartA.java

interface MyClassPartA{
    public default int myMethodA(){return 1;}
}

MyClassPartB.java

interface MyClassPartB{
    public default String myMethodB(){return "B";}
}

and combine them:

MyClass.java

public class MyClass implements MyClassPartA, MyClassPartB{}

and use them:

MyClass myClass = new MyClass();

System.out.println(myClass.myMethodA());
System.out.println(myClass.myMethodB());

You can even pass variables between classes/files with abstract getters and setters that you will need to realize/override in the main class, or a superclass of that however.

Answer 3

This might be a good idea if the class is really so large such that the implemented concepts are not easy to grasp. I see two different ways to do this:

1. Use inheritance: Move general concepts of the class to a base class and derive a specialized class from it.

2. Use aggregation: Move parts of your class to a separate class and establish a relationship to the second class using a reference.

As previously mentioned, there is no concept like partial classes in Java, so you really have to use these OOP mechanisms.

Answer 4

Using just javac, this is not possible. You could of course combine multiple files into a single .java file as part of your build process, and invoke javac afterwards, but that would be cumbersome on so many levels that it is unlikely to be useful.

Maybe you could explain your problem, then we can help better.

If you feel your .java files are too large, you should probably consider refactoring.