Convert COBOL Merge Sort to Java Implementation

[devin-ai-integration]

Convert COBOL Merge Sort to Java Implementation

Summary

This PR adds a Java implementation of the existing COBOL merge sort program in merge_sort/merge_sort_test.cbl. The Java version replicates the exact functionality and output format of the COBOL program:

Key Components Added:

• Customer.java - Record class with fixed-width string formatting (135 chars per record)
• MergeSortJava.java - Main program implementing the same 3-phase workflow as COBOL
• README.md - Documentation comparing both implementations

Program Flow (identical to COBOL):

1. Generate test data files (6 east region + 5 west region customer records)
2. Merge files by ascending customer ID → merge-output.txt
3. Sort merged file by descending contract ID → sorted-contract-id.txt

Output Verification: diff command shows zero differences between COBOL and Java console output and generated files.

Review & Testing Checklist for Human

• Critical: Run both programs side-by-side - Execute ./merge_sort_test and java MergeSortJava to verify outputs are truly identical
• Validate fixed-width parsing logic - Check Customer.fromFixedWidthString() substring indices: (0,5), (5,55), (55,105), (105,110), (110,135) against COBOL record definition
• Test with modified data - Try changing a customer record in COBOL to verify Java handles different data correctly
• Verify file contents match exactly - Compare test-file-1.txt, test-file-2.txt, merge-output.txt, sorted-contract-id.txt between both implementations
• Test sort orders - Confirm merge produces ascending customer ID order and sort produces descending contract ID order

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    COBOL["merge_sort_test.cbl<br/>Original COBOL Program"]:::context
    CustomerJava["Customer.java<br/>Record Class"]:::major-edit
    MergeSortJava["MergeSortJava.java<br/>Main Program"]:::major-edit
    README["README.md<br/>Documentation"]:::major-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 by Customer ID"]:::context
    SortOutput["sorted-contract-id.txt<br/>Sorted by Contract ID"]:::context
    
    COBOL -->|"generates"| TestFile1
    COBOL -->|"generates"| TestFile2
    COBOL -->|"creates"| MergeOutput
    COBOL -->|"creates"| SortOutput
    
    MergeSortJava -->|"uses"| CustomerJava
    MergeSortJava -->|"replicates behavior"| COBOL
    MergeSortJava -->|"generates identical"| TestFile1
    MergeSortJava -->|"generates identical"| 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

• Fixed-width formatting is critical - Each customer record is exactly 135 characters with specific field widths matching COBOL's pic clauses
• Test data is hardcoded - Both implementations use identical hardcoded customer records for reproducible testing
• File-based operations - Unlike typical Java collections-based sorting, this maintains COBOL's file I/O approach for authentic behavior replication
• Error handling - Java version uses System.exit(1) to match COBOL's error behavior

Link to Devin run: https://app.devin.ai/sessions/470daf8b12904ef09f63ccce7ad52515
Requested by: @schaudhry123

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