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I have just begun to explore Java and do not understand the difference between a project and a file. In essence, do I need to create different projects for each of my programs, or can I simply create new files within an project?

Jainil Ajmera
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  • Which IDE are you talking about? – josivan Mar 20 '16 at 02:04
  • Most IDEs are trying to help preserve our sanity by requiring from us organizing our code (java files and other resources) inside projects. So each java file should be part of some project (even if your IDE doesn't require it try to organize it that way yourself). – Pshemo Mar 20 '16 at 02:06
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    I am using Eclipse, and understand that each java file must be a part of some project. However, my question is: Do I have to create a new project for each new program? – Jainil Ajmera Mar 20 '16 at 02:09
  • No, you don't *have to* but it doesn't mean you shouldn't. For instance I have one project for Stack Overflow questions in which I separate questions in packages and place code from questions there (later I can delete these packages if I don't need them). But if you want to create few applications it usually is better to split them in separate projects (You can later reuse code/resources from one project as part of another projects http://stackoverflow.com/a/11792925/1393766). – Pshemo Mar 20 '16 at 02:15
  • Is there any other purpose for creating projects than to organize files? – Jainil Ajmera Mar 20 '16 at 04:43

3 Answers3

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A project has nothing to do with Java. It is a construct your IDE uses to help you manage different things you're working on.

A project usually

  • will consist of a set of files in one or multiple directories, and
  • have a host of settings to do with that "project," including, but not limited to, which version of Java to use, editor settings like whether to default to tabs or spaces, memory you allocate to it during runtime, what source control it uses, which main class to use when the project is run (or multiple ways to run it), etc.

A file

  • has code in it (for the purposes of your question)
  • in Java corresponds to one class
  • has zero or one, but not multiple, main methods, so there's only one way to run it at most

It may be easier to create a separate project for each different main method you will need to run. I can't recall which is easier though. It's certainly a good way to start thinking about whether two things might better fit in different "projects."

And my actual advice is to not use an IDE at all for your first few programs. This teaches you what the language and compiler do and what the IDE does. Right now you are confused whether "projects" are part of Java, which is one reason I recommend this.

djechlin
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  • I started with notepad and compiled from command line. Looking back It think that was very helpful as well. The IDE does too much for you when you're first learning. – Mark W Mar 20 '16 at 03:13
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Do I need to create different projects for each of my programs, or can I simply create new files within an project?

By "file" I assume you are referring to class source code files, and specifically source code files that have a public static void main(String[]) entry point method.

The answer is that you CAN create many such "main" classes in a project in an IDE.

Whether you SHOULD do this depends on your application packaging requirements; e.g. whether you want one JAR file or multiple JAR files, and / or whether you want to treat different parts of if your codebase as separate / separable for the purposes of version control, build control, release control, etcetera.

Stephen C
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A Java project would usually contain a number of files, most being Java class files. (These have the ".java" extension.) Other files would include a build file, image files, etc. Each ".java" file defines a Class. A Class is something that can be instantiated. (Think of spawning) When you instantiate a Class it becomes an object with attributes and methods, or things that it does. Java programs work by instantiating these classes as objects and asking them to "do" things.

Now to your question of "projects". There are many different Java developer tools called IDEs. These IDEs organize your Java files into what you could think of as a project.The term project is rather nebulous here because some IDEs, like Eclipse, use a project as a grouping under another concept called a workspace. Other IDEs, such as IntelliJ use the term "project" to refer to everything you are working on while creating other "group" concepts called modules. In the end the terms, "workspace", "project", and "module" all refer to some way that your developer tool organizes all of the files you are working with.

Cliff
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