Java string to math equation
<p>I need to implement function <code>public int eval(String infix) {...}</code>
and when I use this like this:</p>

<pre><code>eval("3+2*(4+5)") 
</code></pre>

<p>I must receive 21. </p>

<p>The arithmetic expression can contain '+', '*' and parentheses.</p>

<p>So, how can I convert this to math equation? <strong>I can't use non-standard libs.</strong></p>

<p><strong>UPDATE:
Solution found.</strong></p>

<p><strong>It is 2 way: Polish Notation and using ScriptEngine.</strong></p>

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