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

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Exception in thread “main” java.lang.NoSuchMethodError: main

public class m
{
    int a; //class variable


    void f1()
    {
       int b=10;
       System.out.println(a);
       System.out.println(b);
    }
}
class B
{
   public static void main(String args[])
   {
      m ob=new m(); //object created
      ob.f1(); //calling f1 method

   }
}

Hi, welcome at Stackoverflow. We would appreciate if you take a *bit* more effort in asking the question the smart way in the future :) — BalusC, Jun 04 '10 at 02:18
This Community Wiki question lists the possible causes of this common problem: http://stackoverflow.com/questions/5407250/causes-of-java-lang-nosuchmethoderror-main-exception-in-thread-main — Stephen C, Jun 28 '11 at 14:37

score 5 · Answer 1 · answered Jun 04 '10 at 02:26

I'll guess.

You are trying to invoke:

java m

Since you defined you main method in class B you should call

java B

To execute it.

Here's my test:

$cat >m.java<<. 
> public class m
> {
>     int a; //class variable
>     void f1()
>     {
>        int b=10;
>        System.out.println(a);
>        System.out.println(b);
>     }
> }
> class B
> {
>    public static void main(String args[])
>    {
>       m ob=new m(); //object created
>       ob.f1(); //calling f1 method
>    }
> }
> .
$javac m.java 
$java m 
Exception in thread "main" java.lang.NoSuchMethodError: main
$java B
0
10
$

If you see, invoking java B prints 0 10as expected.

BTW this would be a more aligned Java style format: http://pastebin.com/qPvwVZi1 — OscarRyz, Jun 04 '10 at 02:29

score 2 · Answer 2 · answered Jun 04 '10 at 02:13

2

Main needs to be in the top-level class whose name corresponds to the filename - so if "m" is the name of your file that's where main needs to be. Note that by convention class names start with an uppercase letter.

answered Jun 04 '10 at 02:13

JRL

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Not necessarily, the `main` method could be in class `B` it is just, `B` needs to be invoked not `m` – OscarRyz Jun 04 '10 at 02:32

score 1 · Answer 3 · answered Jun 04 '10 at 02:32

Did you invoke the Java program with java m? The main method is defined in the class B, not m, therefore, you need the java B command to invoke it. It may be confusing if you reasoned by "Same as filename.".

Also, putting two classes in one file may be a bad practice.

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

3 Answers3