Class has no main method

  package helloworldapp;
  
  public class first
  {
      class J_Employee
      {
          public int m_workYear;
  
          public J_Employee()
          {
              m_workYear = 1;
          }
      }
  
      public class J_Teacher extends J_Employee
      {
          public int m_classHour;
  
          public J_Teacher()
          {
              m_classHour = 96;
          }
          public void mb_printInfo()
          {
              System.out.println("该教师的工作年限为"+m_workYear);
              System.out.println("该教师的授课课时为"+m_classHour);
          }
          public static void main(String args[])
          {
              J_Teacher tom = new J_Teacher();
              tom.mb_printInfo();
          }
      }
      
  }
  

Examples of books
What is wrong ? ? If the main place outside the class , does not work, seek solutions ! !
------ Solution ---------------------------------------- ----
landlord right main move out, and then changed to the following:

    public static void main(String args[])
      {
      	PolymorphismTest pltt=new PolymorphismTest();
          PolymorphismTest.J_Teacher tom=pltt.new J_Teacher();
          tom.mb_printInfo();
      }
  

This should clearly know why the wrong bar ?
------ For reference only -------------------------------------- -
main (String args [])

should be String [] args
------ For reference only -------------------------- -------------
I prawn up ! !