在Codenvy上使用Java创建“Hello World”

Question

Before you read, understand I'm clearly a noob (Actually, I don't even know anything about programming yet). I wanted to start learning-practicing with Java using an online IDE. In this case, I'm using Codenvy (www.codenvy.com). It's clearly beautiful and awesome, but I have a question. In Eclipse or DrJava or whatever (simple IDEs), to make "Hello World", you need to do this...

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

As said on websites like this: http://goo.gl/vYhP83

On Codenvy, it looks to be "harder" (obviously, it's easy when you know, but harder in the meaning that there're more things to do). On samples of Hello World, I see folders, packages, .xml and external libraries. Can somebody tell me how to do (step by step if possible, without ignoring anything, I'm a noob after all) "Hello World" on Codenvy? And explain me why it's different from Eclipse, for example. Please, don't say "Go to Eclipse, you're drunk". I want to understand Codenvy, I think I will learn from understanding Codenvy. Thanks you.

Answer 1

Codenvy uses Maven and Ant as default build managers. Your app has to be packaged as JAR and this JAR is then executed. Thus, you need to have pom.xml or build.xml file in your project.

The best way for you to get started is to create a sample app from the project wizard - Maven Console.

It's a bit different from Eclipse where all you need is your class and Java installed.

Answer 2

This is tutorial for simple Java "Hello World":

http://www.smlcodes.com/tutorials/codenvy-java-onepage-tutorial

At step 4 I had to make googling this tutorial.

Answer 3

So, in order to run any compiled languages (such as Java), your code needs to be compiled. You can compile/build your project with Maven/Ant, but indeed this can be a bit cumbersome if you quickly want to script and test something. Many IDE's can quickly compile and run a single class for you when you press run.

Although it seems codenvy does not come with this functionality by default, we can easily script compiling and running a file. Go to commands and add a new one (by pressing '+'). Within the command line field enter:

javac ${explorer.current.file.path}; 
SP=${project.java.sourcepath}; 
cd ../${current.project.path}/${SP//:/ }[0];
java ${current.class.fqn};

Here we basically ask java to compile the selected file and to run it afterwards (probably someone can come up with a more sophisticated way to do this, but at least it should give you some basic functionality).

Note: If you depend on multiple java files, you will have to compile those too, at this point it may become easier to go trough an online tutorial on how to use Ant.