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They treat char values from the surrogate ranges as undefined characters. For example, Character.isLetter('\uD840') returns false, even though this specific value if followed by any low-surrogate value in a string would represent a letter.

Compliant Solution

This noncompliant code example compliant solution corrects the problem with supplementary characters by using the integer form of the Character.isLetter() method that accepts a Unicode code point as an int argument. Java library methods that accept an int value support all Unicode characters, including supplementary characters.  

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Forming strings consisting of partial characters can result in unexpected behavior.

Automated Detection

Bibliography

[API 2014]	Classes Character and BreakIterator
[Java Tutorials]	Character Boundaries
[Seacord 2015]	Image Modified STR01-J. Do not assume that a Java char fully represents a Unicode code point LiveLesson

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