Android Studio could not find or load main class of “Scratch” file

问题

Update: Below problem is remained until Android Studio 3.4.2.

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I use Android Studio 3.3 and created a scratch file (File > new > Scratch File > Java). The IDE created scratch.java in ~/.AndroidStudio3.3/config/scratches:

class Scratch {
    public static void main(String[] args) {

    }
}

But when I run that scratch file ( by pressing green button near to the class name or main method), I get this error:

Error: Could not find or load main class Scratch

I think that IDE does not make Scratch.class and so Java cannot find it. Is there a way for solving this problem and running scratch files from IDE (without using Terminal)?

回答1:

Update

I just noticed that this issue was fixed in Android Studio 3.5!

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The only way I got this to work (in Android Studio 3.4.1) is this very dirty approach:

1. Go to Run > Edit Configurations > Scratch
2. In Before launch at the bottom add (+) Run External tool

3. In External Tools popup press + and fill in the following Tool Settings

   Name: Compile Scratch

   Program: javac

   Arguments: $FileName$

   Working Directory: your scratch file directory

4. Press OK

5. Again in External Tools popup press + and fill in the following Tool Settings

   Name: Run Scratch

   Program: java

   Arguments: $FileClass$

   Working Directory: your scratch file directory

6. Press OK and Apply in Run/Debug Configurations

Weirdly this works only if you use the green arrows beside the class/main declaration. If you use the Run button in the menu this also fails.

You will still get the not found error in the Scratch tab of the run window. But two additional tabs will pop up (one for each external tool). In the Run Scratch tab you will get your output.

I personally don't like this, But it's the best workaround I came up with.

来源：https://stackoverflow.com/questions/54322086/android-studio-could-not-find-or-load-main-class-of-scratch-file