Milestone 1: 1 — Project Foundation and Core Email Slicing

[mcode-app-dev]

View Milestone

---

Table of Contents

• Status
• Feature Overview
• Testing
• Architecture
• Suggested Order of Review

---

Status

Milestone 1 was successfully completed. All goals defined in the Milestone Instructions were implemented:

• Maven project scaffolding with Maven Wrapper
• EmailSliceResult record, EmailSlicer parsing logic, and Main CLI entry point
• JUnit 5 unit tests covering valid emails, missing @, empty/blank input, whitespace trimming, and edge cases

Deviation from Milestone Instructions: A Messages.java class was added to centralize all user-facing strings. This was not explicitly called for in the spec but is a minor structural improvement that aids maintainability and future localization without changing any external behavior.

The initial validation strategy uses contains("@") (matching the original Python behavior), as prescribed by the Milestone Instructions for this milestone, with regex-based validation deferred to Milestone 2.

---

Feature Overview

This milestone establishes the complete Java 17 Maven project and implements core email slicing functionality, migrating the original Python emailSlicer.py to an idiomatic Java CLI application.

End-user capability: A user can run the application, enter an email address at the prompt, and see the username and domain printed to the console — matching the original Python tool's behavior.

Example session:

$ java -jar target/email-slicer.jar
Please enter your Email Id:
user@example.com
Your username is:  user
Your domain is:  example.com

---

Testing

Automated Testing

EmailSlicerTest.java contains 14 JUnit 5 tests organized into nested test classes:

Category	Tests	Description
Valid emails	3	Simple email, dotted username, plus addressing
Whitespace handling	2	Leading/trailing spaces, tabs/mixed whitespace
Missing @	2	No @ symbol, plain word
Empty/blank input	3	Null, empty string, blank string
Edge cases	5	@ only, @ at start, @ at end, multiple @, three-part @
Error messages	1	Verifies user-friendly error message text

Run tests with:

./mvnw test

Manual Testing

1. Build the project:

   ./mvnw package

2. Run the JAR:

   java -jar target/email-slicer.jar

3. Enter user@example.com — verify output:

   Your username is:  user
   Your domain is:  example.com
   

4. Enter invalidemail — verify output:

   Please enter a valid Email Id.
   

   and a non-zero exit code (echo $? should print 1).

---

Architecture

Overview

graph TD
    subgraph Legend
        L1[New]:::newNode
        L2[Reference Only]:::refNode
    end

    A["emailSlicer.py<br/>(Original Python Script)"]:::refNode
    B["Main.java<br/>(CLI Entry Point)"]:::newNode
    C["EmailSlicer.java<br/>(Parsing Logic)"]:::newNode
    D["EmailSliceResult.java<br/>(Record)"]:::newNode
    E["Messages.java<br/>(User-Facing Strings)"]:::newNode
    F["pom.xml + Maven Wrapper<br/>(Build System)"]:::newNode

    A -.->|"migrated to"| B
    B -->|"delegates to"| C
    C -->|"returns"| D
    B -->|"uses"| E
    C -->|"uses"| E
    F -->|"builds"| B
    F -->|"builds"| C

    classDef newNode fill:#90EE90,stroke:#333,color:#000
    classDef refNode fill:#D3D3D3,stroke:#333,color:#000

Loading

Changes

Build System (pom.xml + Maven Wrapper)

• pom.xml configured with groupId=com.emailslicer, artifactId=email-slicer, targeting Java 17
• Dependencies: JUnit 5.10.2 (test scope only)
• Plugins: maven-compiler-plugin 3.11.0, maven-surefire-plugin 3.2.5, maven-jar-plugin 3.3.0 (with Main as manifest main class, final name email-slicer)
• Maven Wrapper (mvnw/mvnw.cmd + .mvn/wrapper/) checked in for zero-install builds
• .gitignore configured for Maven target/, IDE files, and OS artifacts

Parsing Logic (EmailSlicer.java)

• Utility class with private constructor; single static method slice(String email)
• Trims input via String.strip() (matching Python's strip() behavior)
• Validates presence of @ using contains("@") — matching original Python validation
• Splits on the first @ using indexOf + substring
• Throws IllegalArgumentException with a user-friendly message for null, blank, or missing-@ input

Data Carrier (EmailSliceResult.java)

• Java 17 record with two fields: username and domain
• Provides immutability and auto-generated equals/hashCode/toString

CLI Entry Point (Main.java)

• Reads email from System.in via Scanner, delegates to EmailSlicer.slice()
• Prints formatted username and domain using System.out.printf
• Catches IllegalArgumentException, prints the error message, and exits with code 1

User-Facing Strings (Messages.java)

• Constants-only utility class centralizing all prompt text, error messages, and format strings
• Referenced by both Main and EmailSlicer to ensure consistent messaging

Design Decisions

1. Two-class separation of parsing logic and console I/O

• EmailSlicer contains pure parsing logic; Main handles all I/O
• Justification: Enables unit testing of parsing without mocking System.in/System.out. Prescribed by the Modernization Instructions.

2. Initial validation matches Python behavior (contains("@"))

• The simpler check was chosen for this milestone to achieve behavioral parity first
• Justification: Keeps this milestone focused on project scaffolding and structure. Regex-based validation is deferred to Milestone 2 as specified in the Milestone Instructions.

3. IllegalArgumentException for invalid input signaling

• Chosen over Optional.empty() return type
• Justification: Aligns with the project's error handling guidelines. Makes test assertions straightforward via assertThrows. Provides descriptive error messages to end users.

4. Dedicated Messages class for user-facing strings

• All prompt text, error messages, and format strings extracted into Messages.java
• Justification: Avoids string duplication across Main and EmailSlicer, simplifies future localization, and makes message content easily reviewable in one place.

---

Suggested Order of Review

1. pom.xml — Build configuration, dependencies, and plugins
2. src/main/java/com/emailslicer/EmailSliceResult.java — Data carrier record (simplest class; introduces the core data model)
3. src/main/java/com/emailslicer/Messages.java — User-facing string constants (referenced by the next two files)
4. src/main/java/com/emailslicer/EmailSlicer.java — Core parsing logic (uses EmailSliceResult and Messages)
5. src/main/java/com/emailslicer/Main.java — CLI entry point (uses all of the above)
6. src/test/java/com/emailslicer/EmailSlicerTest.java — Unit tests (validates the parsing logic)
7. .gitignore — Repository ignore rules