Milestone 1: 1 — Project Scaffold, Core Email Parsing, and CLI Entry Point

[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 scope items from the Milestone Instructions are implemented:

• Maven project initialized with standard directory layout and Maven Wrapper
• EmailParts Java 17 record implemented
• EmailSlicer.parse() static method with validation (null/blank, missing @, multiple @, empty username, empty domain)
• Main CLI entry point matching the original Python output format
• JUnit 5 test suite with 8 passing tests covering happy-path and error cases

Deviations from Milestone Instructions: None. The output format of the Java CLI matches the Python original exactly (including the trailing space produced by Python's comma-separated print). A Messages class was added per the error handling guidelines to centralize user-facing strings; this was not explicitly listed in the Milestone Instructions but is prescribed by the project-level instruction file on error handling.

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Feature Overview

This milestone establishes the Java 17 Email Slicer project — a 1:1 migration of the Python emailSlicer.py CLI tool. The application:

• Prompts the user for an email address via stdin
• Validates the input contains exactly one @ with non-empty username and domain parts
• Prints Your username is: <username> and Your domain is: <domain> to stdout
• Prints Please enter a valid Email Id. and exits with code 1 on invalid input

A user can build and run the application with:

./mvnw package && java -jar target/email-slicer.jar

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Testing

Automated testing

EmailSlicerTest.java contains 8 JUnit 5 tests exercising EmailSlicer.parse() directly:

Test	Input	Expectation
validEmail	avimax37@gmail.com	Returns EmailParts("avimax37", "gmail.com")
leadingTrailingWhitespace	user@example.org	Returns EmailParts("user", "example.org")
missingAtSign	invalidemail	Throws IllegalArgumentException
emptyString	""	Throws IllegalArgumentException
nullInput	null	Throws IllegalArgumentException
multipleAtSigns	a@b@c.com	Throws IllegalArgumentException
emptyUsername	@domain.com	Throws IllegalArgumentException
emptyDomain	user@	Throws IllegalArgumentException

Run with: ./mvnw test

Manual testing

1. Build the project:

   cd emailslicer-dkasargod-java && ./mvnw package
   

2. Run with a valid email:

   echo "avimax37@gmail.com" | java -jar target/email-slicer.jar
   

   Expected output:

   Please enter your Email Id:
   Your username is:  avimax37
   Your domain is:  gmail.com
   

3. Run with an invalid email:

   echo "invalidemail" | java -jar target/email-slicer.jar
   

   Expected output:

   Please enter your Email Id:
   Please enter a valid Email Id.
   

   The process should exit with code 1.
4. Compare outputs with the Python original:

   echo "avimax37@gmail.com" | python3 emailSlicer.py
   

   Both should produce identical output.

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Architecture

Overview

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

    subgraph "emailslicer-dkasargod (Python - Reference)"
        PY[emailSlicer.py]:::refNode
    end

    subgraph "emailslicer-dkasargod-java (Java 17)"
        MAIN[Main.java - CLI Entry Point]:::newNode
        SLICER[EmailSlicer.java - Parse Logic]:::newNode
        PARTS[EmailParts.java - Record]:::newNode
        MSGS[Messages.java - Constants]:::newNode
    end

    PY -.->|migrated to| MAIN
    MAIN --> SLICER
    SLICER --> PARTS
    MAIN --> MSGS
    SLICER --> MSGS

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

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Changes

CLI Entry Point (Main.java)

Handles all console I/O: prints the prompt, reads a line from stdin, delegates to EmailSlicer.parse(), and prints the result. On invalid input, catches IllegalArgumentException, prints the error message, and calls System.exit(1).

Parse Logic (EmailSlicer.java)

Contains a single static method parse(String): EmailParts that encapsulates all validation and splitting logic. Validates that input is non-null/non-blank, contains exactly one @, and has non-empty username and domain segments. Throws IllegalArgumentException on any violation.

Result Record (EmailParts.java)

A Java 17 record holding username and domain. Provides immutability and automatic equals/hashCode/toString, which simplifies test assertions.

User-Facing Messages (Messages.java)

Centralizes all user-facing strings (PROMPT_MESSAGE, INVALID_EMAIL_MESSAGE, USERNAME_PREFIX, DOMAIN_PREFIX) as public static final constants, per the error handling guidelines.

Build Configuration (pom.xml, Maven Wrapper)

Maven pom.xml targets Java 17, declares JUnit 5 as the sole (test-scoped) dependency, and configures maven-jar-plugin to produce an executable JAR with Main-Class manifest entry. The Maven Wrapper (mvnw, mvnw.cmd, .mvn/wrapper/maven-wrapper.properties) enables building without a pre-installed Maven.

Design Decisions

1. Separation of parsing logic from I/O

   • Description: EmailSlicer (pure function) is separated from Main (console I/O).
   • Justification: The Python original mixes input()/print() with string slicing. Separating these concerns allows unit testing the parse logic directly without mocking System.in/System.out.

2. Java 17 record for result type

   • Description: EmailParts is declared as a record rather than a POJO.
   • Justification: Records are the idiomatic Java 17 approach for immutable value objects. They provide equals/hashCode/toString automatically, enabling concise assertEquals assertions in tests.

3. IllegalArgumentException for invalid input

   • Description: EmailSlicer.parse() throws IllegalArgumentException on invalid input; Main catches it and prints the message.
   • Justification: Aligns with the error handling guidelines, which prescribe IllegalArgumentException for precondition violations. Produces clean assertThrows test assertions and establishes a convention for future validation enhancements.

4. Centralized Messages class

   • Description: All user-facing strings are stored as constants in Messages.java.
   • Justification: Required by the error handling guidelines. Avoids string duplication between production code and tests, and provides a single place to update output text.

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Suggested Order of Review

1. emailslicer-dkasargod-java/pom.xml — Build configuration, dependencies, and packaging
2. emailslicer-dkasargod-java/.mvn/wrapper/maven-wrapper.properties — Maven Wrapper configuration
3. emailslicer-dkasargod-java/mvnw — Maven Wrapper shell script
4. emailslicer-dkasargod-java/src/main/java/com/emailslicer/EmailParts.java — Data model (record)
5. emailslicer-dkasargod-java/src/main/java/com/emailslicer/Messages.java — Constants used across the app
6. emailslicer-dkasargod-java/src/main/java/com/emailslicer/EmailSlicer.java — Core parse logic
7. emailslicer-dkasargod-java/src/main/java/com/emailslicer/Main.java — CLI entry point consuming the above
8. emailslicer-dkasargod-java/src/test/java/com/emailslicer/EmailSlicerTest.java — Test suite validating parse logic