title: What does '0' do in Java?
body: <p>I'm trying to find the product of all digits in a number, which I have stored as a string (due to int and long length limits).</p>
  
  <p>So the number looks like this:</p>
  
  <pre><code>final String number = "1234567898765432123......etc"
  </code></pre>
  
  <p>If I use this code, it works:</p>
  
  <pre><code>product *= number.charAt(i + j) - '0';
  </code></pre>
  
  <p>It doesn't if I remove the '0'.</p>
  
  <p>I got this code from another online resource. Can someone explain what the '0' does?</p>