Unable to run Java code with Intellij IDEA

问题:

I have just downloaded the IDE, and I want to edit my first Java file with it, I'm not interested in creating a whole project, just editing the single file.

So I opened the file from my desktop with Intellij IDEA as I set it as my default program for opening .java files.

I write some code and the main run and debug buttons are greyed out! I can't run my code!

I have already installed Java 8 update 45 64-bit (I have a 64 bit OS) as well as the Java development kit (J8U45). I have set my global IDE SDK as my JDK installation, and when it prompts me I also set this as my project SDK, but still the run and debug buttons are unable to be used!

Edit: I am also unable to run my file regardless of if its in a project or not.

Edit 2: Screenshot of my project setup

回答1:

Move your code inside of the src folder. Once it's there, it'll be compiled on-the-fly every time it's saved.

IntelliJ only recognizes files in specific locations as part of the project - namely, anything inside of a blue folder is specifically considered to be source code.

Also - while I can't see all of your source code - be sure that it's proper Java syntax, with a class declared the same as the file and that it has a main method (specifically public static void main(String[] args)). IntelliJ won't run code without a main method (rather, it can't - neither it nor Java would know where to start).

回答2:

My classes contained a main() method yet I was unable to see the Run option. That option was enabled once I marked a folder containing my class files as a source folder:

1. Right click the folder containing your source
2. Select Mark Directory as → Test Source Root

Some of the classes in my folder don't have a main() method, but I still see a Run option for those.

回答3:

right click on the "SRC folder", select "Mark directory as:, select "Resource Root".

Then Edit the run configuration. select Run, run, edit configuration, with the plus button add an application configuration, give it a name (could be any name), and in the main class write down the full name of the main java class for example, com.example.java.MaxValues.

you might also need to check file, project structure, project settings-project, give it a folder for the compiler output, preferably a separate folder, under the java folder,

回答4:

Don't forget the "String[] args" in your main method. Otherwise, there's no option to run your program.

public static void main(String[] args){

}

回答5:

If you are just opened a new java project then create a new folder src/ in the man project location.

Then cut and paste all your package in that folder.

Then Right click on src directory and select option Mark Directory As > Sources Root.