Convert COBOL merge sort implementation to Java

[devin-ai-integration]

Convert COBOL merge sort implementation to Java

Summary

This PR adds a complete Java implementation that replicates the functionality of the existing COBOL merge sort program (merge_sort/merge_sort_test.cbl). The implementation includes:

• CustomerRecord class: Implements Comparable<CustomerRecord> with fields matching the COBOL record structure (customer ID, names, contract ID, comment)
• MergeSortProcessor: Handles file operations, merging sorted files by customer ID ascending, and sorting by contract ID descending
• MergeSortMain: Main application that creates test data, executes merge/sort operations, and displays results
• Complete workflow: Matches COBOL flow - create test data → merge files → sort by contract ID → display results

The Java version uses in-memory Collections instead of direct file processing, leveraging Java's built-in sorting capabilities while maintaining the same logical behavior and output format as the original COBOL implementation.

Review & Testing Checklist for Human

• Verify output format matches COBOL exactly - Compare the fixed-width string formatting (CustomerRecord.toString()) against COBOL output to ensure field widths and padding are identical
• Test the merge logic with edge cases - Verify merging works correctly with empty files, files of different sizes, and duplicate customer IDs
• Validate sort correctness - Confirm that contract ID sorting is truly in descending order and handles ties appropriately
• Run end-to-end test - Execute the Java program and compare complete output against running the original COBOL program to ensure identical behavior

Recommended test plan: Compile and run java com.example.mergesort.MergeSortMain and verify the output shows correct customer ID ascending merge (1,3,5,10,24,25,30,50,75,85,999) followed by contract ID descending sort (12323,8765,7725,5423,5050,4567,3331,1610,1175,653,247).

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    COBOL["merge_sort/merge_sort_test.cbl"]:::context
    CustomerRecord["java-merge-sort/src/.../CustomerRecord.java"]:::major-edit
    MergeSortProcessor["java-merge-sort/src/.../MergeSortProcessor.java"]:::major-edit
    MergeSortMain["java-merge-sort/src/.../MergeSortMain.java"]:::major-edit
    README["java-merge-sort/README.md"]:::major-edit
    
    COBOL -->|"converted to"| CustomerRecord
    COBOL -->|"logic replicated in"| MergeSortProcessor
    COBOL -->|"workflow replicated in"| MergeSortMain
    
    CustomerRecord -->|"used by"| MergeSortProcessor
    MergeSortProcessor -->|"used by"| MergeSortMain
    
    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

• The implementation successfully compiled and ran, producing the expected merge and sort output
• Fixed-width string formatting is critical - the toString() method in CustomerRecord uses specific field widths (5,50,50,5,25) to match COBOL PIC clauses
• Test data exactly matches the COBOL version for validation purposes
• Generated output files (.txt) and compiled classes (.class) were intentionally excluded from the commit

Link to Devin run: https://app.devin.ai/sessions/7351953a888a46b5bef1232524732046
Requested by: @schaudhry123

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