I read his explanation but I don't have a great understanding of why a JVM would need to clean up like this. Doesn't it have a Garbage collector just for that?

I read his explanation but I don't have a great understanding of why a JVM would need to clean up like this. Doesn't it have a Garbage collector just for that? Why does it get slower over time? The only thing I know that gets slower over time without you doing anything special is my dad's mac os x word-only macbook pro.