Add Java implementation of COBOL merge sort program

[devin-ai-integration]

Java Implementation of COBOL merge_sort_test.cbl Program

Summary

This PR implements a complete Java port of the COBOL merge_sort_test.cbl program, creating four core Java classes that replicate the exact functionality and output format of the original COBOL version.

Key Components Added:

• CustomerRecord.java: Data structure with fixed-width field formatting (customerID: 5 digits, lastName/firstName: 50 chars each, contractID: 5 digits, comment: 25 chars)
• FileReader.java & FileWriter.java: Handle fixed-width record I/O with exact COBOL file format compatibility
• MergeSortProcessor.java: Main program implementing merge (ascending customerID) and sort (descending contractID) operations

Critical Fix Applied: The initial implementation produced records with trailing spaces (136 chars vs COBOL's 120 chars). Fixed by trimming output records and updating the parser to handle variable-length input records.

Verification Status: All output files now produce byte-for-byte identical results between COBOL and Java versions, confirmed via diff comparison.

Review & Testing Checklist for Human

• Run both COBOL and Java versions locally and verify identical outputs - Most critical test to ensure business logic parity
• Verify merge operation sorts on ascending customerID - Check first few records in merge-output.txt match expected order
• Verify sort operation uses descending contractID - Check sorted-contract-id.txt has highest contractID first
• Test with different data - Modify test data values to ensure sorting logic works beyond hardcoded values
• Verify error handling - Test behavior when input files are missing or corrupted

Recommended Test Plan:

1. Clean all output files: rm *.txt && rm java/*.txt
2. Run COBOL version: cd merge_sort && ./merge_sort_test
3. Run Java version: cd java && java MergeSortProcessor
4. Compare all outputs: diff ../test-file-1.txt test-file-1.txt (repeat for all 4 files)
5. Verify file sizes match exactly: wc -c *.txt ../*.txt

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TB
    COBOL["merge_sort_test.cbl<br/>(Original COBOL)"]:::context
    
    Main["MergeSortProcessor.java<br/>(Main Program)"]:::major-edit
    Record["CustomerRecord.java<br/>(Data Structure)"]:::major-edit
    Reader["FileReader.java<br/>(File Input)"]:::major-edit
    Writer["FileWriter.java<br/>(File Output)"]:::major-edit
    
    TestFile1["test-file-1.txt"]:::context
    TestFile2["test-file-2.txt"]:::context
    MergeOutput["merge-output.txt"]:::context
    SortedOutput["sorted-contract-id.txt"]:::context
    
    Main -->|"generates test data"| Writer
    Writer --> TestFile1
    Writer --> TestFile2
    
    Main -->|"reads input files"| Reader
    Reader --> TestFile1
    Reader --> TestFile2
    
    Main -->|"writes merged results"| Writer
    Writer --> MergeOutput
    
    Main -->|"writes sorted results"| Writer  
    Writer --> SortedOutput
    
    Record -->|"used by all components"| Main
    Record --> Reader
    Record --> Writer
    
    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

• Ticket Reference: MBA-18
• Session Link: https://app.devin.ai/sessions/09918119e9f04ccaab5fe1b3c299cc37
• Requested by: @ibrahim-sowunmi
• Testing Confidence: High - Both versions produce identical console output and file contents verified with diff
• Risk Level: Medium - Complete language port with complex fixed-width formatting requirements

Technical Details:

• Fixed-width records: 135 characters total (before trimming trailing spaces)
• Output format: Records trimmed to remove trailing spaces (matches COBOL behavior)
• Parser handles both full-length (135 char) and trimmed records for compatibility
• All numeric fields zero-padded, text fields space-padded to specified lengths

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