Compile Error: Line: 3, Column: 30 Only top-level class methods can be declared static

Question

I get this error whenever I run the below code:

Error - Only top-level class methods can be declared static

Code

public class ContactSearch 
{
    public static List<Contact> searchForContacts(String lastName, String mailCode)
    {
       return [SELECT Id, Name, LastName, MailingPostalCode 
               FROM Contact 
               WHERE LastName = :lastName AND MailingPostalCode = :mailCode];

    } 
}

Does anyone know why this is happening? I can't find the issue. I ran the accounts code the same way and it worked so I am confused with this error message.

(I tried to look for the answer in previous posts, but none applied to my case, therefore I am posing this new question.)

Answer 1

If you're declaring an inner class, all of its methods must be stateful:

public class TopLevel
{
    public class InnerClass
    {
        public List<Contact> search_WillCompile()
        {
            // this method declaration is valid
            // implementation details ommitted
        }
        public static List<Contact> search_WillNotCompile()
        {
            // this method declaration is invalid
        }
    }
}

That's in contrast to methods on a top level class, whose method declarations will compile either way:

public class TopLevel
{
    public static void staticMethod() { }
    public void statefulMethod() { }
}

If you're working within an Execute Anonymous window, all declared classes are virtual inner classes.