title: What does UnmappableCharacterException mean?
body: <p><a href="http://java.sun.com/javase/6/docs/api/java/nio/charset/CharsetDecoder.html" rel="nofollow noreferrer">CharsetDecoder</a> reads:</p>
  
  <blockquote>
    <p>There are two general types of decoding errors. If the input byte sequence is not legal for this charset then the input is considered <i>malformed</i>. If the input byte sequence is legal but cannot be mapped to a valid Unicode character then an <i>unmappable character</i> has been encountered.</p>
  </blockquote>
  
  <p>I understand the concept of malformed characters, but what does an unmappable character mean? I thought that Unicode contains all possible characters. How then could a legal byte sequence not be mappable to a Unicode character?</p>