Example 3.4 Form-Centric Validation

/**If the first name or last name fields were left
  blank, then an error will be returned to client.
  With this strategy, these checks for the existence
  of a required field are duplicated. If this validation
  logic were abstracted into a separate component,
  it could be reused across forms (see
  Validation Based on Abstract Types strategy)**/
public Vector validate()
{
Vector errorCollection = new Vector();
    if ((firstname == null) ||
   (firstname.trim.length() < 1))
     errorCollection.addElement("firstname required");
    if ((lastname == null) || (lastname.trim.length()
  < 1))
     errorCollection.addElement("lastname required");
return errorCollection;
}