The following basic how tos are intended to help you get started using Java in IntelliJ IDEA.
Moving source files into a subfolder
You shouldn't keep your source (.java) files in the project root directory. If this is, currently, the case, create a subdirectory in the project root directory and move all your source files into that subdirectory.
Enabling coding assistance for .java files
Coding assistance for Java turns on automatically as soon as you mark the folder with your .java files as containing source code. In the Project tool window (), right-click the folder, point to Mark Directory as and select Sources Root.
Making the Java API accessible to your code
When writing in Java, you, generally, reuse (i.e. reference) the Java API classes. These classes are available in a JDK. So, to make the Java API accessible to your code, you should download and then specify your JDK:
- Open your .java file in the editor: select the file in the Project tool window and press F4.
- Click Setup SDK.
- In the dialog that opens, select your JDK and click OK, or click Configure, click , select JDK, and then select the directory where you have the desired JDK installed.
Creating a folder structure for your package or specifying a package prefix
If you don't have an appropriate folder structure for your package yet (let's assume that the name of your package is
com.example.mypackage), you have two options leading to about the same result:
- Create the corresponding folder structure in your source directory (e.g.
- Assign your source folder a package prefix without actually creating the folder structure:
Making classes in a JAR accessible to your app
Say, you have a JAR with the classes that you want to reuse in your app. In that case, you should add the JAR to the dependencies of your module. As a result, the JAR classes become available for referencing in your code, and they are included in your app when you build it.
- Open the Project Structure dialog (e.g. Ctrl+Shift+Alt+S), select Modules and select your module.
- Select the Dependencies tab, click and select JARs or directories.
- In the dialog that opens, select your JAR file.
Compiling .java files
If compilation is problematic, IntelliJ IDEA will inform you about the reason and provide hints for fixing the problem.
Running your app
If the compilation is a success, you can run your app:
- Open the class with a main() method in the editor.
- In the left margin, next to the main() method, click the run marker (the green arrow) and select Run '<ClassName>.main()'.
Packaging your app in a JAR
To package your app in a JAR, you should configure a JAR artifact and then build it:
- Open the Project Structure dialog (Ctrl+Shift+Alt+S) and select Artifacts.
- Click , select JAR and select From modules with dependencies.
- In the dialog that opens, select the class with a main() method (the Main Class field).
- Save the artifact settings by clicking OK in the Project Structure dialog.
- Select Build | Build Artifacts, select your artifact and select Build. (If there's only one artifact, you can just press Enter when the Build Artifact menu pops up.)