[kevin9327]

HexToOct.hexToDecimal looks each character up with indexOf and uses the result directly, so a character that is not a hex digit adds -1 instead of failing. The method then returns a wrong number with no error:

• hexToDecimal("1G") returns 15 (16 * 1 + -1)
• hexToDecimal("0x1A") returns -230
• hexToOctal("Z") returns 0 (the -1 makes decimalToOctal skip its loop)

This change throws IllegalArgumentException for any character outside 0-9A-F (after the existing upper-casing), matching what OctalToHexadecimal.octalToDecimal already does for bad octal digits. Valid inputs give the same results as before.

HexToOctTest.testInvalidHexDigitThrows covers the three inputs above. It fails on master and passes with this change; the existing tests still pass.

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations. (no new algorithm)
• All new algorithms include a corresponding test class that validates their functionality. (test added to the existing class)
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

I used an AI assistant while preparing this change; I reviewed the code and ran the tests myself.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.34%. Comparing base (b2af1db) to head (91ad22a).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7748   +/-   ##
=========================================
  Coverage     82.33%   82.34%           
- Complexity     8444     8445    +1     
=========================================
  Files           843      843           
  Lines         26154    26156    +2     
  Branches       5109     5110    +1     
=========================================
+ Hits          21535    21537    +2     
  Misses         3830     3830           
  Partials        789      789           

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[alxkm]

Looks good, thanks for the contribution.