title: Addition method to java class
body: <p>Let's say I have a Money class that looks like this: </p>
  
  <pre><code>public class Money {
      private BigDecimal amount;
      private Currency currency;
  }
  </code></pre>
  
  <p>I'd like to add two of these classes together, e.g.</p>
  
  <pre><code>Money m1 = Money(5);
  Money m2 = Money(10);
  Money m3 = m1+m2; // m3.amount should be 15
  </code></pre>
  
  <p>How would I write a method so that I could add together two of these Money classes?</p>