Migrate COBOL merge sort program to Java

[devin-ai-integration]

Migrate COBOL merge sort program to Java

Summary

This PR migrates the existing COBOL merge sort program (merge_sort/merge_sort_test.cbl) to Java while preserving the file-based sorting approach and exact functionality. The implementation creates a CustomerRecord class with the same field structure as the COBOL program and implements external file-based merge and sort operations rather than using in-memory collections.

Key Components:

• CustomerRecord.java - Data structure matching COBOL record layout with fixed-width file serialization
• FileMergeSorter.java - Core merge and sort operations using file I/O
• MergeSortExample.java - Main entry point replicating COBOL program flow
• README.md - Comprehensive documentation with COBOL comparison

Behavior Preserved:

• Creates two test data files with identical records to COBOL version
• Merges files and sorts by ascending customer ID
• Sorts merged file by descending customer contract ID
• Uses file-based external sorting for large dataset compatibility

Review & Testing Checklist for Human

• Verify output consistency - Run both COBOL and Java versions and compare the displayed output and generated files to ensure identical results
• Test fixed-width formatting - Check that the CustomerRecord serialization produces correct field widths (5-50-50-5-25 characters) and handles padding properly
• Validate sort operations - Confirm merge sorts by ascending customer ID and final sort is descending by contract ID
• Test error handling - Try with missing/corrupted input files to ensure proper exception handling
• Performance with large files - Test with larger datasets to verify the file-based approach works for external sorting scenarios

Recommended Test Plan:

1. Run the original COBOL program and capture output
2. Run the Java implementation and compare outputs
3. Manually inspect the generated .txt files for format correctness
4. Test with modified input data to verify sorting logic

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    COBOL["merge_sort_test.cbl"]:::context
    
    CustomerRecord["CustomerRecord.java<br/>Data structure & serialization"]:::major-edit
    FileMergeSorter["FileMergeSorter.java<br/>Core merge/sort operations"]:::major-edit
    MergeSortExample["MergeSortExample.java<br/>Main program entry point"]:::major-edit
    README["README.md<br/>Documentation"]:::minor-edit
    
    TestFile1["test-file-1.txt<br/>East region data"]:::context
    TestFile2["test-file-2.txt<br/>West region data"]:::context
    MergeOutput["merge-output.txt<br/>Merged & sorted by ID"]:::context
    SortedOutput["sorted-contract-id.txt<br/>Sorted by contract ID desc"]:::context
    
    COBOL -.->|"migrated to"| MergeSortExample
    MergeSortExample --> FileMergeSorter
    FileMergeSorter --> CustomerRecord
    
    FileMergeSorter -->|"creates"| TestFile1
    FileMergeSorter -->|"creates"| TestFile2
    FileMergeSorter -->|"merges to"| MergeOutput
    FileMergeSorter -->|"sorts to"| SortedOutput
    
    CustomerRecord -->|"serializes to"| TestFile1
    CustomerRecord -->|"serializes to"| TestFile2
    
    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 uses external file-based sorting to match COBOL's approach rather than loading everything into memory
• Fixed-width string formatting mimics COBOL PIC clauses but uses Java string manipulation
• Test data exactly matches the COBOL program's hardcoded customer records
• Error handling uses Java exceptions instead of COBOL file status codes

Link to Devin run: https://app.devin.ai/sessions/1b508ed0eecf47b9a63318a1222a926f
Requested by: @schaudhry123

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