Add Java implementation of COBOL merge sort with file-based operations

[devin-ai-integration]

Add Java implementation of COBOL merge sort with file-based operations

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 Java implementation maintains the same file-based approach and produces identical output to the original COBOL program.

Key Changes:

• Created java-merge-sort/ directory with Java implementation
• CustomerRecord.java: Data model matching COBOL's 5-field customer record structure
• MergeSortProgram.java: Main program implementing merge and sort operations using file I/O
• Comprehensive documentation explaining the implementation approach
• Verified output matches COBOL program exactly using diff commands

Functionality Replicated:

1. Generate test data in two files (6 records + 5 records)
2. Merge files sorted by customer ID ascending
3. Sort merged file by contract ID descending
4. File-based operations using BufferedReader/BufferedWriter

Review & Testing Checklist for Human

• Verify identical output: Run both COBOL and Java programs, compare all 4 output files using diff to ensure exact match
• Test with different data: Try modifying test data or adding more records to verify sorting logic works correctly
• Review file format specification: Confirm fixed-width format (5+50+50+5+25 chars) matches COBOL exactly, including padding and field alignment
• Check sorting algorithms: Verify ascending customer ID merge and descending contract ID sort produce expected order
• Test resource management: Ensure files are properly closed and no resource leaks occur with larger datasets

Recommended Test Plan:

1. Clean output files: rm *.txt in both directories
2. Run COBOL: cd merge_sort && ./merge_sort_test
3. Run Java: cd java-merge-sort && java MergeSortProgram
4. Compare: diff merge_sort/*.txt java-merge-sort/*.txt
5. Test with modified data to verify sorting logic

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    COBOL["merge_sort/<br/>merge_sort_test.cbl"]:::context
    
    CustomerRecord["java-merge-sort/<br/>CustomerRecord.java"]:::major-edit
    MergeSort["java-merge-sort/<br/>MergeSortProgram.java"]:::major-edit
    README["java-merge-sort/<br/>README.md"]:::major-edit
    
    TestFile1["test-file-1.txt<br/>(6 records)"]:::context
    TestFile2["test-file-2.txt<br/>(5 records)"]:::context
    MergeOutput["merge-output.txt<br/>(sorted by customer ID)"]:::context
    SortOutput["sorted-contract-id.txt<br/>(sorted by contract ID)"]:::context
    
    COBOL -.-> CustomerRecord
    CustomerRecord --> MergeSort
    MergeSort --> TestFile1
    MergeSort --> TestFile2
    TestFile1 --> MergeOutput
    TestFile2 --> MergeOutput
    MergeOutput --> SortOutput
    
    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:#F5F5F5

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Notes

• Verification Status: All output files verified to match COBOL program exactly using diff
• File Format: Uses fixed-width format with proper zero-padding for numeric fields and left-alignment for text fields
• External Sorting: Implementation supports file-based operations suitable for larger datasets
• Resource Management: Uses try-with-resources blocks for proper file handle management

Link to Devin run: https://app.devin.ai/sessions/57cd1803bcc3436da6ca115e248897ee
Requested by: @schaudhry123 (Samir Chaudhry)

[devin-ai-integration]

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