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https://issues.apache.org/jira/browse/MATH-1681?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ruiqi Dong resolved MATH-1681.
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Resolution: Fixed
> ComplexFormat.parse(String) returns null instead of throwing
> MathParseException for invalid complex number strings
> ------------------------------------------------------------------------------------------------------------------
>
> Key: MATH-1681
> URL: https://issues.apache.org/jira/browse/MATH-1681
> Project: Commons Math
> Issue Type: Bug
> Components: legacy
> Affects Versions: 4.0-beta1
> Reporter: Ruiqi Dong
> Priority: Critical
> Original Estimate: 0.5h
> Remaining Estimate: 0.5h
>
> The {{ComplexFormat.parse(String source)}} method violates its documented
> contract by returning {{null}} instead of throwing {{MathParseException}} for
> certain malformed complex number strings. According to the JavaDoc, the
> method should "throw MathParseException if the beginning of the specified
> string cannot be parsed," but it fails to do so in several cases.
>
> *Test Case to Demonstrate the Bug:*
> {code:java}
> @Test
> public void
> testParseShouldThrowExceptionForInvalidComplexMissingImaginaryCharacter() {
> ComplexFormat format = new ComplexFormat();
> String invalidComplex = "3 + 5";
>
> assertThrows(MathParseException.class, () -> {
> format.parse(invalidComplex);
> }, "Parsing '3 + 5' should throw MathParseException due to missing
> imaginary character 'i'");
> } {code}
> *Test Result:*
> {code:java}
> org.opentest4j.AssertionFailedError: Expected
> org.apache.commons.math4.legacy.exception.MathParseException to be thrown,
> but nothing was thrown.{code}
> *Root Cause Analysis:*
> The bug occurs due to incomplete error handling in the interaction between
> {{parse(String)}} and {{parse(String, ParsePosition)}} methods.
> When parsing "3 + 5":
> # The parser successfully reads "3" (real part), advancing the index from 0
> to 1
> # It reads "+" (operator), advancing the index further
> # It reads "5" (imaginary coefficient), advancing the index to 5
> # It fails to find the imaginary character 'i'
> # At this point, {{parse(String, ParsePosition)}} returns {{null}} BUT does
> not reset the position index
> {code:java}
> // In parse(String source, ParsePosition pos)
> // parse imaginary character
> if (!CompositeFormat.parseFixedstring(source, getImaginaryCharacter(), pos)) {
> return null; // Bug: position index is not reset to initialIndex
> }{code}
> 6. Back in {{{}parse(String){}}}, the check {{if
> (parsePosition.getIndex() == 0)}} evaluates to false (index is 5)
> 7. The method returns {{null}} without throwing an exception
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