title: Modify field in class during runtime - java
body: <p>My question is, is it possible to inject properties or even methods into a already "classloaded" class. I already noticed, that in java it is not really simple to add properties dynamically and everyone says that you should use a Map (<a href="https://stackoverflow.com/questions/4323328/add-property-for-a-object-dynamicly">add property for a object dynamicly</a>). </p>
  
  <p>Is there any better and "cleaner" way to change a class during runtime. I read something about ASM, but i do not know if the visitor pattern, which is use by ASM, is the optimal way to work with. </p>
  
  <p>In case <a href="http://asm.ow2.org/index.html" rel="nofollow noreferrer">ASM</a> is the best thing to handle this problem, is there any documentation beside the one provided on the ASM Website (<a href="http://download.forge.objectweb.org/asm/asm4-guide.pdf" rel="nofollow noreferrer">http://download.forge.objectweb.org/asm/asm4-guide.pdf</a>)</p>