Java programming error - NoSuchMethodError: main

[solarjeep]

I've searched the forums for similar problems but none seem the same scenario as mine, just the same outcome (same error message).

I'm using java version 1.6. I'm learning java. I've been writing several simple programs for several days. They compile fine. Run fine. Until today.

I create a new program, compile it with no errors. Run it and get this error:

"Exception in thread "main" java.lang.NoSuchMethodError: main"

I run a program that I created, compiled and ran yesterday and it runs fine again today. If I recompile it (no errors) it won't run. Same error message.

Here is one of the programs copied from my Root.java file (this is from a book I'm using to learn Java):



class Root {
public static void main(String[] arguments){
int number = 625;
System.out.println("The square root of "
+ number
+ " is "
+ Math.sqrt(number) ) ;
}
}



The most important thing is that everything was working fine yesterday. Same programs today run unless I recompile them. I haven't changed anything. Help!

[Ragazzo]

How are you compiling and trying to run it?

[solarjeep]

from console:

compile:

javac Root.java

run:

java Root

I'm in the directory with the *.java and *.class files. This is the same way I've been doing it for a week now without a problem.

[Enselic]

Make sure the compiler and the VM have the same (major) version, i.e. compare javac -version with java -version. If you use 1.6, both compiler and VM should be of this version.

[solarjeep]

ok, I checked that. Here's the output (I'm not sure the proper way to "quote" this here I hope this is right.

checking java version output =



java -version
java version "1.6.0"
Java(TM) SE Runtime Environment (build 1.6.0-b105)
Java HotSpot(TM) Client VM (build 1.6.0-b105, mixed mode)


checking javac version output =



javac -version
javac 1.6.0

[solarjeep]

On a wild guess -

I created a source file in a different folder. It compiled AND ran correctly.
Hmm.
So, I went to my original folder and deleted all the files in it (about 40 files). Created a new program and it compiled and ran correctly. Created a couple more and no problems. Moved all the original files back to the original folder. Tried to compile and run programs - I get the same error as before. Delete all the files but one or two, they compile and run with no errors.

This is wierd. It seems that there is a limit to the number of files I can have in a folder until I start getting errors in running a java program. I'm not sure what the threshold is (between 6 and 40). What's the connection?

I'm not going to mark this as resolved yet since I have only found a workaround not a solution. Anyone have any ideas?

[dxxvi]

What does

echo $CLASSPATH

say?

[Ragazzo]

Do you have only one class per file (public and non-public)? For example if you have

Test.java:


class Test {
public static void main(String[] args) {
System.out.println("hello world");
}
}


Test2.java


class Test2 {
public static void main(String[] args) {
}
}
class Test {
}


~> javac Test.java
~> java Test
hello world
~> javac Test2.java
~> java Test
Exception in thread "main" java.lang.NoSuchMethodError: main

[solarjeep]

What does

echo $CLASSPATH

say?

I get nothing. A blank line then back to prompt.

[solarjeep]

Do you have only one class per file (public and non-public)?

Yes, only one class per file. Everything I have done so far is very basic.

[Ragazzo]

Yes, only one class per file. Everything I have done so far is very basic.

If you run "javap -verbose Root" and "javap -verbose OldRoot", where Root is the non-working version and OldRoot is the working one, it should print some info about the class files. Look for SourceFile, minor version and major version at the top of the listing and check if there is any difference in them.