Sample Code Before public class Person { private String emailAddress; // Primitive Obsession public void setEmailAddress(String emailAddress) { // Duplicated code if (!emailAddress.matches( "^[\\w.%+-]+@[\\w.-]+\\.[a-zA-Z]{2,}$")) { throw new IllegalArgumentException( "Invalid email address format"); } this.emailAddress = emailAddress; } } public class JobApplication { private String applicantEmailAddress; public void setApplicantEmailAddress(String emailAddress) { // Duplicated code if (!emailAddress.matches( "^[\\w.%+-]+@[\\w.-]+\\.[a-zA-Z]{2,}$")) { throw new IllegalArgumentException( "Invalid email address format"); } this.applicantEmailAddress = emailAddress; } } After public class EmailAddress { // 2. Create an `EmailAddress` class to encapsulate validation rules. private final String value; public EmailAddress(String value) { // The rules are in a single place // And all objects are created valid if (!value.matches("^[\\w.%+-]+@[\\w.-]+\\.[a-zA-Z]{2,}$")) { throw new IllegalArgumentException( "Invalid email address format"); } this.value = value; } } public class Person { private final EmailAddress emailAddress; public Person(EmailAddress emailAddress) { // 1. Identify where email validation logic is duplicated. // 3. Refactor code to use the `Email Address` // class instead of raw strings. // No validation is required this.emailAddress = emailAddress; } } public class JobApplication { private EmailAddress applicantEmailAddress; public JobApplication(EmailAddress applicantEmailAddress) { this.applicantEmailAddress = applicantEmailAddress; } } Type

[x] Semi-Automatic

Safety

This refactoring is safe if you replace all occurrences of raw email strings with the 'EmailAddress' class and ensure all tests pass.

Why Is the Code Better?

You make email validation consistent across your application.

\ Since validation rules are centralized in one place, the code becomes easier to maintain.

\ You also reduce the risk of bugs caused by inconsistent logic.

\ In the real world, Email Addresses are small objects that exist and are not strings.

\ The refactored code is closer to the real-world MAPPER.

\ Notice that bijection names are essential. It would help to create an EmailAddress, not an Email, since the Email should map to the actual message.

\ Don't let Premature Optimizators tell you this solution has a performance penalty.

\ They never do actual benchmarks with real-world data.

Refactor With AI

| Without Proper Instructions | With Specific Instructions | |----|----| | ChatGPT | ChatGPT | | Claude | Claude | | Perplexity | Perplexity | | Copilot | Copilot | | Gemini | Gemini |