I've recently installed Scala as a part of my functional programming course and I've encountered a problem: IntelliJ IDEA 2017.2.1 (Java version 9, build 9+181) doesn't run any of my scala code, exitting with
Error: Could not find or load main class Main
This code is an example.
object Main {
def length[A](list:List[A]):Int = {
if (list == Nil) 0
else 1 + length(list.tail)
}
def main(args: Array[String]): Unit = {
length(List[Int](1, 4, 5, 12, -1))
}
}
It's really simple, yet IntelliJ refuses to run it. Windows CMD doesn't even react to a scala command, resulting into
'scala' is not recognized as an internal or external command,
operable program or batch file.
even though I have it installed on my computer. If I call Scala Console inside of IntelliJ everything works fine and compiles as expected. I've tried switching to JDK 1.8 inside of IntelliJ, yet it led to no result.
What could be the problem?
For me it turns out that the src/main was not marked as Sources Root
which causes the following error
...
One of the two will be used. Which one is undefined.
Error: Could not find or load main class Main
Process finished with exit code 1
So of course after I mark the src/main as Sources Root, the Scala Hello World example runs happy again.
Notice the blue color of directory src/main when it's marked as Sources Root
Are you using the little green arrow to run the program from inside of your Main object?
How did you create the program? It could be that your build file SBT configuration of the project is a different Scala version than what's installed on your computer.
It's really simple, yet IntelliJ refuses to run it. Windows CMD
doesn't even react to a scala command, resulting into
'scala' is not recognized as an internal or external command, operable program or batch file.
This means that Scala is not added to your class path in your terminal. Look up how to do that and see if that doesn't help out your IntelliJ problem too.
I have read every post I can find. I have Eclipse Mars release 4.5.1 and MinGW GCC ver 4.8.1
I have done the following:
Create new workspace.
Created File > New > C++ Project.>Executable>Hello World
Built and Run successfully
added the line
auto i = 6;
The IDE shows
'auto' changes meaning in C++11; please remove it [-
Wc++0x-compat]
I then went to project>C/C++ Build>Settings>Tool Settings>GCC C++ Compiler>Dialect>Language standard and selected C++11.
I also went to project>C/C++ General>Preprocessor Include Path>Providers Select CDT GCC Built-in Compiler Settings and untick “Use global provider...” box then add –std=c++0x
Finally I chose Project>Refresh and Project>Index>Rebuild
But still the error on auto.
Is this Wc++0x-compat switch a problem? Where do I find it?
What else should I do?
I am using the Dart plugin for Eclipse (not the standalone Dart Editor).
How do I configure the project/build so that static type warnings appear as errors in the Eclipse "Problems" tab? For example, this line of code actually compiles, which seems ludicrous:
int newtodo = new LIElement();
Running dartanalyzer at the command line gives an error, as desired:
dartanalyzer foo.dart
But instead of having to run dartanalyzer at the command line (or discovering them at runtime), I would like to have these errors reported on-the-fly in Eclipse.
If this doesn't produce a warning this is a bug according to this discussion new user question. type warnings as errors in Eclipse
(Also initiated from #Justin M. Keyes)
This feels silly, but its been 2 days...somewhere after upgrading from Ubuntu 10.04 to 10.11 and from Eclipse Helios to Eclipse Indigo, I got stuck with the following problem:
Problem Description:
I'm trying to use a function in math.h called isinf(), but the problem also occurs with things like isnan(). The program compiles fine on the command line using make and fine in eclipse using build. But if I open the program file in eclipse it reports that it cannot reolve the isinf() function call. If I just insert the program contents into a new project and new source file, the error appears immediately. This problem did not occur under 11.04 with Eclipse Helios CDT
Questions:
Why are these errors only reported when the program file is opened and not on when the program is compiled; why are the errors not detected make is run from the command line? Is there a solution/workaround available?
Version Info
Linux Ubuntu 10.11 64-bit
Eclipse CDT Indigo, Service Release 1, Build id: 20110916-0149
(Also using Eclipse EE Indigo – if that makes a difference)
GNU Make 3.81
gcc 4.6.1-9Ubuntu3
To Duplicate:
Please find the two files you'll need to replicate below:
Step 0. Verify that everything is fine outside of Eclipse
Copy the attached source file and make file
create a directory e.g. Mkdir FunTest
Save the source file a 'Test.cpp' and the makefile as 'makefile'
Open a command prompt and navigate to the directory e.g. FunTest
Enter 'make'
Enter ./TestOut
Program responds “is not infinite”
Step 1. Create the project in Eclipse
Open Eclipse
Select File|New|MakeFile Project with Existing Code
Click Browse – navigate to the directory (FunTest) and click ok
Select 'Linux GCC' from the Toolchain selector
Click Finish
Step 2. Find the Error
Click Build All (Ctrl-B) – project builds without errors
Open the project in the project explorer to display the file in the directory
Double click on the file “Test.cpp”
Note the error icon next to line testing for infinity
Note the 2 error messages:
Semantic error: Function _isinff could not be resolved
Semantic error: Function _isinfl could not be resolved
Test.cpp:
include <math.h>
int main(int argc, char **argv)
{
int TestNum = 10;
if (isinf(TestNum) == 0)
printf("Not infinite\n");
return 0;
}
makefile:
# Specify the compiler
CC = g++
# Specify the compiler flags
CFLAGS += -c
# Specify the files making up the application
SOURCES = Test.cpp
OBJECTS = $(SOURCES:.cpp=.o)
EXECUTABLE = TestOut
all: $(EXECUTABLE)
$(EXECUTABLE): $(OBJECTS)
$(CC) $(LDFLAGS) $(OBJECTS) $(LDLIBS) -o $#
.cpp.o:
$(CC) $(CPPFLAGS) $(CFLAGS) $< -o $#
install:
#echo "Build complete!"
I have experienced similar problems of the CDT reporting errors even though the code compiled fine within Eclipse Indigo.
Project > Properties > Settings > Binary Parsers > "GNU Elf Parser"
helped in my case. I had the "Elf Parser" checked.
That looks like a problem that many others have had with eclipse CDT before. Sometimes shutting eclipse down and then starting it back up again is enough to help. If that isn't the case, take a look at what I have below:
Compilation ok, but eclipse content assist having problems
Check your includes: if you're using include<math.h> change it to include<cmath>. The same for stdio.h and stdlib.h, you should replace by cstdio and cstdlib. Another option may be change you project to a C project instead of a C++.
You are missing -lm option in your build preferences.
Project->Properties->Settings->Miscleanous->Other (linker) flags[]
For me, it was solved by adding a specific ‘Source Location’ folder, and removing the default. In Luna, it is under:
Project > Properties > C/C++ General > Paths and Symbols > Source
Location
I have installed Eclipse 3.5.2 and today's Scala plugin from /update-current (that's Scala 2.8 final.) I can compile and run Scala projects consisting of a single singleton object that implements main().
But, if a project contains more classes, I receive the "Could not find the main class" error.
I have tried searching for the solution and I discovered:
Eclipse is correctly looking for the Main$ class, not the Main class
* under Debug Configurations, my main class is correctly identified as mypackage.Main
* my plugin is up to date and recommended for my version of Eclipse
* cleaning, restarting etc. doesn't help.
The same project will compile with scalac.
Thanks for any ideas on how to solve this.
EDIT: MatthieuF suggested I should post the code.
This snippet produces an error. It's not the most idiomatic code, but I wrote it that way to test my environment. I tried it as a single file and as separate files. It DOES work with scalac.
import swing._
class HelloFrame extends Frame {
title = "First program"
contents = new Label("Hello, world!")
}
object Hello {
val frame = new HelloFrame
def main(args : Array[String]) : Unit = {
frame.visible = true
}
}
BUT, if I nest the definition of HelloFrame within Hello, it works. This snippet runs perfectly:
import swing._
object Hello {
class HelloFrame extends Frame {
title = "First program"
contents = new Label("Hello, world!")
}
val frame = new HelloFrame
def main(args : Array[String]) : Unit = {
frame.visible = true
}
}
For me, the problem was that there was a build error (see Problems tab) which was preventing compilation; oops! The reason you see the error is that the run macro proceeds despite the failed compilation step, and attempts to run class files it expects to be there; they don't exist because there was a build error preventing compilation, so it says it can't find Main (not compiled).
Problem goes away when build can complete successfully, i.e. errors are fixed.
I guess, theoretically, there may be more complicated reasons your build is not completing successfully that are not listed in Problems.
One possibility is that you are trying to launch using ctrl-F11, but from a different class.
The Scala Eclipse plugin does not obey the defaults for Java launching. In Preferences->Run/Debug->Launching, there are some options Launch Operation->Always Launch the previously selected application, etc. This currently does not work in the Scala eclipse plugin. To launch a specified main, you need to launch it from the editor for the class.
There has been a bug raised for this. http://scala-ide.assembla.com/spaces/scala-ide/tickets/1000023-scala-launch--does-not-follow-jdt-behaviour
EDIT: This is now (mostly) fixed.
For me it was Eclipse specific problem. I noticed that .class file wasn't built at all. So bin directory doesn't have compiled classes.
When I manually compiled *.scala file using *.sbt and copied it to bin directory it was working as expected.
I tried different tips and tricks and it wasn't worked until I reinstalled Scala plugin in Eclipse .
I'd solve similar problem by executig "Project->Clean.." with next automatically building.
I had the same error message with a Java application made by myself.
The problem was that I deleted (though inside Eclipse) a jar that belonged to the Java build path, without deleting it from the Java build path (project's Properties window). When I did it the class could compile and run again.
Make sure that the .class files exist, usually below the bin directory.
In particular, if you have errors in unrelated files in the same project then the compilation may fail, and no .class files will be produced.
There can be the case of projects, containing errors, added to the build path of the application which prevents the completion of successful compilation. Make sure you remove any such project from the build path before running the application.
Removing these projects solved the problem for me.
Do you have a proper build tool setup? Like sbt have you installed it?
You can check its version by $sbt --version
If it is not setup you can download from here http://www.scala-sbt.org/download.html
You might have to restart your eclipse after installation.
Just copy your XXX.scala file code. Remove the package and create a new Scala Class. Paste your XXX.scala code. (If you are using maven, do a maven clean and build.) Run configuration again. This works for me.
I have faced this issue. I have just deleted the package name, created scala class, Written the same code, Set Build to "Build Automatically". Finally, It works perfectly fine.
Check scala-ide.log
For me the issue was that there were errors on:
AppData\Local\Temp\sbt_10d322fb\xsbt\ClassName.scala:16: error: not found: value enteringPhase
enteringPhase(currentRun.flattenPhase.next) { s fullName separator }
If you are using Intellij, mark directory as source root