Need help! Unable to follow the Sun WBT practice.(Simple program)

Question

Exception in thread "main" java.lang.NoSuchMethodError: main
Due to the above error, I can't follow the Sun's WBT program. I think something is missing in my Java environment since Sun provided instruction should be correct.
Please let me know to troubleshoot this.
Below causes error.(Followed the Sun WBT)
public class Customer {
     public int customerID = 0; // Default ID for the customer
     public char status = 'N'; // default
     public double totalPurchases= 0.0; // default
     // This method displays the value for an item
     public void displayCustomerInfo() {
          System.out.println("Customer ID:" +customerID);
          System.out.println("Status: " +status);
          System.out.println("Purchases: " +totalPurchases);
} // end of display method
} // end of the class
Below works since I did not use WBT instruction:
public class Customer2 {
     public static void main( String args[] ) {
     int customerID = 0; // Default ID for the customer
     char status = 'N'; // default
     double totalPurchases= 0.0; // default
          System.out.println("Customer ID:" +customerID);
          System.out.println("Status: " +status);
          System.out.println("Purchases: " +totalPurchases);
} // end of ????( I do not know how to say here)
} // end of the class

Answer 1

public class Customer {
public int customerID = 0; // Default ID for the customer
public char status = 'N'; // default
public double totalPurchases= 0.0; // default
// This method displays the value for an item
public void displayCustomerInfo() {
System.out.println("Customer ID:" +customerID);
System.out.println("Status: " +status);
System.out.println("Purchases: " +totalPurchases);
} // end of display method
} // end of the class
NOTE: IF I run the above program, it does not run due to exception. I can compile it without error. Since above coding is used in the Sun WBT course, I think I have Java environment problem. Are you able to run the above program?