Java Reference
In-Depth Information
applies a regular expression match against the field value and returns the
Boolean
result of the match. Imagine the following form input fields corresponding to our
FieldType
instances:
<input type="password" name="password" value=""/>
<input type="tel" name="phone" value=""/>
<input type="email" name="email" value=""/>
<input type="text" name="ssn" value=""/>
The value of the input field's
name
attribute will be used to identify the
FieldType
; you used this same name when you instantiated each
FieldType
enum
constant. When a form is submitted, you have access to each input field's
name
and the value that was entered into the field. You need to be able to map the field's
name
to a
FieldType
and call the
validate()
method with the input value. The
class variable,
nameToFieldTypeMap
, is declared and initialized for this purpose.
For each
FieldType enum
constant,
nameToFieldTypeMap
stores an entry
with the field name as the key, and the
FieldType
as the value. The
look-
up(String)
class method uses this map to look up the
FieldType
from the field
name. The code to validate an
email
input field with an input value of
john@doe.com
is quite concise:
// <input type="email" name="email" value="john@doe.com"/>
String fieldName = "email";
String fieldValue = "john@doe.com";
boolean valid
= FieldType.lookup(fieldName).validate(fieldValue);
The
main()
method shows an example validation for each of the
FieldTypes
.
The
printValid()
method prints the field name, field value, and the field's valida-
tion result.
This recipe has demonstrated that there is a lot more potential in the
enum
type
than just the ability to define a set of named constants.
Enum
types have all the power
of a normal class, plus additional features that allow you to create well-encapsulated
and intelligent constants.
