Milestone 1: 1 — Project Scaffolding, Core Email Slicing Logic, and Build Pipeline

[mcode-app-dev]

View Milestone

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Table of Contents

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

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Status

The milestone was successfully completed. All goals specified in the Milestone Instructions — Maven project scaffolding, core email-slicing logic, console I/O, centralized messages, and JUnit 5 unit tests — have been implemented. The build produces an executable JAR and all tests pass.

One intentional deviation from the Modernization Instructions: The Modernization Instructions specify that inputs like "@", "@domain", and "user@" should be rejected as invalid. However, the Milestone Instructions explicitly require matching the Python original's behavior in this milestone (split on first @; only reject inputs lacking @ entirely). The current implementation follows the Milestone Instructions, deferring stricter regex-based validation to Milestone 2.

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Feature Overview

This milestone migrates the Python Email Slicer (emailSlicer.py) to an idiomatic Java 17 console application. The user can:

• Build the project: ./mvnw package
• Run the application: java -jar target/email-slicer.jar
• Enter an email address at the prompt and receive the parsed username and domain as output — matching the Python original's behavior

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Testing

Automated Testing

EmailSlicerTest.java contains 11 test cases (via JUnit 5 parameterized and standard tests) covering:

Category	Cases
Valid emails	avimax37@gmail.com, first.last@example.org, user@mail.example.co.uk
Whitespace stripping	" user@test.com "
Multiple @ signs	"a@b@c.com" — splits on first @, matching Python
Missing @	"invalidemail.com", "justtext"
Null / empty / blank	null, "", " "
Edge cases	"@domain.com", "user@", "@"

Run with: ./mvnw test

Manual Testing

1. Build: ./mvnw package
2. Run: java -jar target/email-slicer.jar
3. Enter avimax37@gmail.com at the prompt
4. Expected output:

   Your username is:  avimax37
   Your domain is:  gmail.com
   

5. Run again with invalidemail.com — expected output: Please enter a valid Email Id.

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Architecture

Overview

graph TD
    subgraph Legend
        L1[Modified]
        L2[New]
    end

    subgraph "Console Application"
        MAIN["Main.java\n(Console I/O Entry Point)"]
        MSGS["Messages.java\n(User-facing Strings)"]
    end

    subgraph "Core Logic"
        SLICER["EmailSlicer.java\n(Parsing Logic)"]
        RESULT["EmailSlicerResult.java\n(Result Record)"]
    end

    subgraph "Build System"
        POM["pom.xml + Maven Wrapper\n(Build Pipeline)"]
    end

    MAIN --> SLICER
    MAIN --> MSGS
    SLICER --> RESULT
    POM --> MAIN

    style L1 fill:#ffff00,color:#000
    style L2 fill:#00cc00,color:#000
    style MAIN fill:#00cc00,color:#000
    style MSGS fill:#00cc00,color:#000
    style SLICER fill:#00cc00,color:#000
    style RESULT fill:#00cc00,color:#000
    style POM fill:#00cc00,color:#000

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Changes

Build System (pom.xml, mvnw, .mvn/)

• Hand-crafted pom.xml with Java 17 compiler settings, JUnit 5.10.2 test dependency, and three plugins: maven-compiler-plugin, maven-surefire-plugin, maven-jar-plugin
• maven-jar-plugin configured with com.emailslicer.Main as the main class, producing target/email-slicer.jar
• Maven Wrapper 3.2.0 (mvnw / mvnw.cmd / .mvn/wrapper/maven-wrapper.properties) checked in for zero-install builds
• .gitignore added for Java/Maven/IDE artifacts

Core Logic (EmailSlicer.java, EmailSlicerResult.java)

• EmailSlicer — final utility class with a single static method slice(String): Optional<EmailSlicerResult>. Strips whitespace, splits on the first @ via indexOf, and returns Optional.empty() for null/blank/missing-@ inputs. No I/O side effects.
• EmailSlicerResult — Java 17 record with two components (username, domain), providing immutable value semantics with auto-generated equals(), hashCode(), toString().

Console Application (Main.java, Messages.java)

• Main — thin I/O shell that prints a prompt, reads one line via Scanner, delegates to EmailSlicer.slice(), and prints the result or an error. Mirrors the Python script's top-level flow.
• Messages — final constants class centralizing all user-facing strings (PROMPT_EMAIL, USERNAME_PREFIX, DOMAIN_PREFIX, INVALID_EMAIL). Output strings match the Python original exactly.

Documentation (README.md)

• Replaced the Python-centric README with a Java 17-oriented version covering build, run, test instructions, example I/O, and project structure.

Design Decisions

1. Hand-crafted minimal POM over archetype generation — The project has only four source files. A generated archetype would introduce unnecessary boilerplate. The hand-crafted pom.xml contains exactly three plugins and one test dependency, keeping configuration minimal and auditable.

2. Separation of I/O from parsing logic — The Python script mixes input()/print() with @-splitting in a single file. The Java version separates Main (I/O) from EmailSlicer (pure logic), making the parsing function independently testable without system-in/system-out capture.

3. Java 17 record for result type — EmailSlicerResult is defined as a record rather than a POJO, leveraging Java 17's concise syntax for immutable data carriers. This eliminates boilerplate while providing correct equals()/hashCode() semantics.

4. Optional return type over null — EmailSlicer.slice() returns Optional<EmailSlicerResult> to explicitly represent invalid input at the type level, avoiding null-pointer errors and making the API self-documenting.

5. Centralized Messages class — All user-facing strings are extracted into Messages.java constants, following the project's error handling guidelines and enabling Milestone 2 to add validation messages without scattering strings across classes.

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Suggested Order of Review

1. pom.xml — Build configuration, dependencies, plugins; establishes the project foundation
2. src/main/java/com/emailslicer/EmailSlicerResult.java — The record type; simplest file, introduces the data model
3. src/main/java/com/emailslicer/EmailSlicer.java — Core parsing logic; consumes the result record
4. src/main/java/com/emailslicer/Messages.java — String constants used by Main
5. src/main/java/com/emailslicer/Main.java — Console entry point; ties together EmailSlicer and Messages
6. src/test/java/com/emailslicer/EmailSlicerTest.java — Unit tests validating the core logic
7. README.md — Updated documentation
8. .gitignore — Housekeeping