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You can test any non-start character with<br />

<pre><code id="code-8147911">System.out.println(Character.isJavaIdentifierPart('#'));</code></pre>
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You can test any non-start character with


System.out.println(Character.isJavaIdentifierPart('#'));

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Thanks CEHJ, but in &nbsp;a certification test scenario , my guess would have been, yes it is valid. It turns out is not, &nbsp;why?. I just have to learn it the way it is? 
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Thanks CEHJ, but in  a certification test scenario , my guess would have been, yes it is valid. It turns out is not,  why?. I just have to learn it the way it is?

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iirc only numbers, letters and underscores. The first of these can't start an identifier
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iirc only numbers, letters and underscores. The first of these can't start an identifier

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Why is int e# an incorrect variable name? if in the end is a letter followed by a character that well could be a connector character, i mean , &nbsp;is not a plus or a minus. 
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Why is int e# an incorrect variable name? if in the end is a letter followed by a character that well could be a connector character, i mean ,  is not a plus or a minus. 

why is int e# an incorrect variable name?

Java is a platform-independent, object-oriented programming language and run-time environment, designed to have as few implementation dependencies as possible such that developers can write one set of code across all platforms using libraries. Most devices will not run Java natively, and require a run-time component to be installed in order to execute a Java program.