Java 7 underscore in numeric literals
<p>When we must use a _ to separate digits in a number I don't' understand the
following case in which I can't use it:</p>

<ul>
<li>In positions where a string of digits 
is expected (as documented in the JDK7 guide <a href="http://docs.oracle.com/javase/7/docs/technotes/guides/language/underscores-literals.html" rel="nofollow">here</a>)</li>
</ul>

<p>Some examples?</p>
