Milestone 1: 1. Project Foundation and Core Email Parsing CLI

[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 described in the Milestone Instructions were implemented: the Maven project was scaffolded with wrapper, the core email parsing logic was separated from console I/O, EmailResult was modeled as a Java 17 record, and a JUnit 5 test suite was added.

Deviation from spec: The Milestone Instructions noted that initial validation in slice() should match the Python original's minimal @-presence check, deferring stricter regex validation to Milestone 2. The implementation follows this approach — slice() checks only for the presence of @ via indexOf, consistent with the Python baseline. Inputs like @domain.com (empty username) and user@ (empty domain) are accepted, matching the Python original's behavior. Tests explicitly document this parity.

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Feature Overview

This milestone migrates the Python emailSlicer.py CLI tool to a Java 17 project (emailslicer-java). The end user can:

• Run ./mvnw compile exec:java to launch the Email Slicer CLI
• Enter an email address at the prompt (e.g., user@domain.com)
• See the parsed username and domain printed to stdout:

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

• See an error message (Please enter a valid Email Id.) for inputs without @

The Java implementation preserves behavioral parity with the Python original while introducing proper class structure, type-safe return values (EmailResult record), and Optional-based null safety.

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Testing

Automated testing

The EmailSlicerTest class contains 16 test cases run via ./mvnw test:

Category	Tests	Description
Valid emails	slice_validEmail_returnsExpectedParts	Parameterized test with 4 valid emails verifying correct username/domain extraction
Whitespace trimming	slice_leadingAndTrailingWhitespace_isTrimmed, slice_tabsAndNewlines_areTrimmed	Verifies strip() parity with Python's strip()
Invalid emails (no @)	slice_noAtSign_returnsEmpty	Parameterized test covering plain strings, empty string, whitespace-only input
Null input	slice_null_returnsEmpty	Null safety via @NullSource
Edge cases (Python parity)	slice_emptyUsername_returnsResult, slice_emptyDomain_returnsResult, slice_multipleAtSigns_splitsOnFirst	Documents that the Python-equivalent behavior is preserved
Record behavior	emailResult_equalsAndHashCode, emailResult_toString_containsFields	Verifies record auto-generated methods

Manual testing

1. From the repository root, run:

   ./mvnw compile exec:java

2. At the Please enter your Email Id: prompt, type alice@example.com and press Enter.
3. Verify the output:

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

4. Run again and enter invalidemail (no @ symbol). Verify the output:

   Please enter a valid Email Id.
   

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Architecture

Overview

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

    subgraph "emailslicer-dkasargod (Python)"
        PY["emailSlicer.py<br/>Python CLI Script"]:::refNode
    end

    subgraph "emailslicer-java (Java 17)"
        MAIN["Main.java<br/>Console I/O"]:::newNode
        SLICER["EmailSlicer.java<br/>Parsing Logic"]:::newNode
        RECORD["EmailResult.java<br/>Java 17 Record"]:::newNode
        POM["pom.xml<br/>Maven Build"]:::newNode
    end

    PY -.->|"migrated to"| MAIN
    MAIN --> SLICER
    SLICER --> RECORD

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

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Changes

Maven Build Configuration (pom.xml)

• New Maven project with groupId=com.emailslicer, artifactId=emailslicer, Java 17 source/target
• JUnit 5.10.2 managed via junit-bom BOM import
• Plugins: maven-compiler-plugin (3.11.0), maven-surefire-plugin (3.2.5), maven-jar-plugin (3.3.0 with Main-Class manifest), exec-maven-plugin (3.1.0)
• Maven Wrapper (3.2.0) bundled via .mvn/wrapper/ and mvnw/mvnw.cmd scripts, targeting Maven 3.9.6

EmailResult Record (EmailResult.java)

• Java 17 record with two fields: username and domain
• Provides immutable value semantics with auto-generated equals(), hashCode(), and toString()
• Replaces the implicit tuple-like return of the Python original

EmailSlicer Parsing Logic (EmailSlicer.java)

• Final utility class with private constructor (non-instantiable)
• Single static method slice(String email) returning Optional<EmailResult>
• Trims input via String.strip() (matching Python's strip()), checks for @ via indexOf, splits into username/domain
• Returns Optional.empty() for null input or missing @

Main Console I/O (Main.java)

• Entry point with Scanner-based stdin reading
• Prompts with "Please enter your Email Id:", delegates to EmailSlicer.slice(), and prints results using ifPresentOrElse
• Output format matches the Python original: "Your username is: ..." / "Your domain is: ..."

Design Decisions

1. Maven with maven-jar-plugin over maven-shade-plugin

   • The maven-jar-plugin with a Main-Class manifest entry was chosen over maven-shade-plugin (fat JAR). Since the project has zero runtime dependencies (JUnit is test-scoped only), a shade plugin adds unnecessary build complexity. The jar plugin satisfies the java -jar target/emailslicer.jar requirement from the Modernization Instructions.

2. Separated concerns (3 classes) over single-class design

   • Main.java handles I/O, EmailSlicer.java holds pure parsing logic, and EmailResult.java is the value type. This separation — rather than mirroring the Python single-script approach — makes the parsing logic independently testable without stdout capture, aligning with the Modernization Instructions.

3. Python-equivalent validation deferred to Milestone 2

   • slice() currently validates only @ presence (matching the Python original's email.find("@") != -1). Inputs like @domain.com or user@ are accepted. This establishes behavioral parity as a baseline; regex-based stricter validation is deferred to Milestone 2 per the Milestone Instructions.

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Suggested Order of Review

1. pom.xml — Start here to understand the build configuration, dependencies, and plugin setup
2. src/main/java/com/emailslicer/EmailResult.java — The Java 17 record that models the parsed result
3. src/main/java/com/emailslicer/EmailSlicer.java — Core parsing logic; the primary API surface
4. src/main/java/com/emailslicer/Main.java — Console I/O entry point that consumes EmailSlicer
5. src/test/java/com/emailslicer/EmailSlicerTest.java — Test suite covering valid, invalid, and edge-case inputs
6. .gitignore, mvnw/mvnw.cmd, .mvn/wrapper/ — Supporting build infrastructure (skim only)