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import java.io.File;

public class Main
{
    public static void main(String[] args)
    {
        File file = new File("./testdir");  // Directory 'testdir' in the current directory
        if(file.isDirectory()){
            if(file.list().length>0){
                System.out.println("Directory is not empty!");
            }else{
                System.out.println("Directory is empty!");
            }
        }else{
            System.out.println("This is not a directory!");
        }
    }
}

Directory D://Java/file.txt is not empty!