Convert COBOL merge sort example to Java (MBA-18)

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Convert COBOL merge sort example to Java (MBA-18)

Summary

Converts the COBOL program merge_sort_test.cbl to an equivalent Java implementation that preserves exact functionality. The Java version replicates the same workflow: creates two test data files with hardcoded customer records, merges them sorted by customer ID (ascending), then sorts by contract ID (descending), displaying records at each step.

Key components:

• CustomerRecord inner class with 5-digit customer/contract IDs, 50-char names, 25-char comments
• Fixed-width string formatting to match COBOL's pic 9(5) and pic x(50) field specifications
• File I/O using BufferedReader/Writer to replicate COBOL's line sequential organization
• Collections.sort() with custom Comparators to replicate COBOL MERGE/SORT behavior
• Identical hardcoded test data (11 total records across 2 files)

Review & Testing Checklist for Human

• Verify fixed-width formatting is correct - Check that toFileString() produces 135-character lines with proper zero-padding for IDs and space-padding for text fields
• Test output file compatibility - Run both COBOL and Java versions and compare the generated files (merge-output.txt, sorted-contract-id.txt) for identical content
• Validate test data accuracy - Cross-reference the 11 hardcoded records in createTestData() against the original COBOL data (lines 185-335)
• Test end-to-end functionality - Compile and run java MergeSortExample to verify console output matches expected merge/sort results

Notes

• No CI checks configured for this repository
• The fromFileString() method uses substring parsing that could be sensitive to field boundary errors
• Java Collections.sort() should be equivalent to COBOL's stable sort behavior

Ticket: MBA-18
Requested by: Eashan Sinha (@eashansinha)
Link to Devin run: https://app.devin.ai/sessions/65ceb1ee8eb542349c35422a6964b3ea

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