Convert COBOL merge sort to Java implementation

[devin-ai-integration]

Convert COBOL merge sort to Java implementation

Summary

This PR converts the COBOL merge sort functionality from merge_sort/merge_sort_test.cbl to a modern Java implementation while preserving the core business logic. The conversion replaces file-based COBOL operations with in-memory Java collections and implements the same merge-by-customer-ID and sort-by-contract-ID-descending operations.

Key Components Added:

• CustomerRecord.java - Java class mapping COBOL record layout with proper field types and formatting
• MergeSortExample.java - Main implementation with merge algorithm, sorting, and test data generation
• README.md - Documentation explaining the conversion and usage instructions

Core Logic Preserved:

• Two-pointer merge algorithm for combining files sorted by customer ID
• Descending sort by contract ID using Java Collections
• Same test data as original COBOL version (11 customer records across 2 files)

Review & Testing Checklist for Human

• Verify output format matches COBOL exactly - Run both implementations and compare the display output character-by-character, especially the fixed-width formatting and padding
• Test merge algorithm edge cases - Verify correct handling when one input list is empty, when all elements from one list come before the other, and when customer IDs are equal
• Confirm sort produces correct descending order by contract ID - Manually verify the contract IDs are in descending order: 12323 → 8765 → 7725 → 5423 → 5050 → 4567 → 3331 → 1610 → 1175 → 653 → 247
• Validate test data accuracy - Cross-reference each customer record between COBOL and Java versions to ensure no transcription errors in IDs, names, contract IDs, or comments
• Compile and run the Java code - Ensure clean compilation and execution with expected output

Recommended Test Plan:

1. Run javac -d . src/main/java/com/example/mergesort/*.java && java com.example.mergesort.MergeSortExample
2. Compare output with expected COBOL behavior (merge by customer ID ascending, then sort by contract ID descending)
3. Verify the "Done." message appears at the end

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    COBOL["merge_sort_test.cbl<br/>(Original COBOL)"]:::context
    
    CustomerRecord["java-merge-sort/src/main/java/<br/>com/example/mergesort/<br/>CustomerRecord.java"]:::major-edit
    MergeSortExample["java-merge-sort/src/main/java/<br/>com/example/mergesort/<br/>MergeSortExample.java"]:::major-edit
    README["java-merge-sort/README.md"]:::major-edit
    
    COBOL -->|"Converted to"| CustomerRecord
    COBOL -->|"Converted to"| MergeSortExample
    
    CustomerRecord -->|"Used by"| MergeSortExample
    MergeSortExample -->|"Creates test data<br/>Merges by customer ID<br/>Sorts by contract ID"| Output["Console Output<br/>(Formatted records)"]:::context
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit  
        L3[Context/No Edit]:::context
    end

    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB
    classDef context fill:#FFFFFF

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Notes

• Field Mapping: COBOL pic 9(5) mapped to Java int, pic x(n) mapped to Java String with proper padding in toString()
• Algorithm Change: Replaced COBOL's built-in MERGE statement with explicit two-pointer merge algorithm
• Memory Model: Converted from file-based processing to in-memory collections for better performance and simplicity
• Testing Limitation: Could not run original COBOL code for direct output comparison due to environment constraints

Link to Devin run: https://app.devin.ai/sessions/0a302785c3114b1294a8a834b33f905e
Requested by: Samir Chaudhry (@schaudhry123)

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