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 Java implementation that replicates the functionality of the existing COBOL merge sort program (merge_sort_test.cbl). The Java version maintains the same three-phase approach: data creation, merge operations, and sort operations, all using file-based I/O rather than in-memory processing.

Key Components Added:

• CustomerRecord.java: Data model matching COBOL record structure with fixed-width formatting
• MergeSortExample.java: Main program implementing the three-phase workflow

Functionality Replicated:

• Creates two test files with 6 and 5 customer records respectively (11 total)
• Merges files by ascending customer ID and displays results
• Re-sorts merged data by descending contract ID and displays results
• Maintains identical console output format and file contents as COBOL version

Review & Testing Checklist for Human

• Critical: Output Verification - Run both COBOL (./merge_sort_test) and Java (java MergeSortExample) programs side-by-side and verify console outputs are identical character-for-character
• Critical: File Content Validation - Compare generated files (test-file-1.txt, test-file-2.txt, merge-output.txt, sorted-contract-id.txt) between COBOL and Java versions using diff
• High: Test Data Accuracy - Manually verify the hardcoded customer records in MergeSortExample.java match exactly with the data creation logic in the COBOL source (lines 185-333)
• Medium: Fixed-Width Formatting - Inspect the toFixedWidthString() and toDisplayString() methods to ensure field widths (5-digit IDs, 50-char names, 25-char comments) match COBOL specifications
• Medium: Sort Order Verification - Confirm merge phase produces ascending customer ID order and sort phase produces descending contract ID order with identical record sequences

Recommended Test Plan:

1. Clean existing output files: rm *.txt
2. Run COBOL version: ./merge_sort_test > cobol_output.txt
3. Clean files again: rm *.txt
4. Run Java version: java MergeSortExample > java_output.txt
5. Compare outputs: diff cobol_output.txt java_output.txt
6. Compare file contents: diff <COBOL_generated_files> <Java_generated_files>

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    COBOL["merge_sort_test.cbl<br/>Original COBOL Implementation"]:::context
    CustomerRecord["CustomerRecord.java<br/>Data Model Class"]:::major-edit
    MergeSortExample["MergeSortExample.java<br/>Main Program Logic"]:::major-edit
    
    TestFile1["test-file-1.txt<br/>6 Customer Records"]:::context
    TestFile2["test-file-2.txt<br/>5 Customer Records"]:::context
    MergedFile["merge-output.txt<br/>11 Records Sorted by Customer ID"]:::context
    SortedFile["sorted-contract-id.txt<br/>11 Records Sorted by Contract ID"]:::context
    
    COBOL -.->|"Replicates functionality"| MergeSortExample
    MergeSortExample -->|"Creates test data"| TestFile1
    MergeSortExample -->|"Creates test data"| TestFile2
    MergeSortExample -->|"Reads & merges"| MergedFile
    MergeSortExample -->|"Reads & sorts"| SortedFile
    CustomerRecord -->|"Used by"| MergeSortExample
    
    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

Risk Assessment: ⚠️ Medium Risk - While the core logic is straightforward, exact formatting replication between COBOL and Java requires careful validation. The fixed-width string formatting and file I/O behavior differences between languages create potential for subtle mismatches.

Session Info:

• Link to Devin run: https://app.devin.ai/sessions/3ca099ebcd3d4ad59bfbc58e73baa936
• Requested by: @schaudhry123

Implementation Notes:

• Java uses String.format() with fixed-width specifiers to match COBOL's PIC clauses
• File I/O uses standard Java BufferedReader/PrintWriter for line-sequential file processing
• Sort operations use Java Collections.sort() with custom Comparators
• All test data is hardcoded to match exact values from COBOL source

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