Advantages of using DNSResolver

[Guru Prashanth Thanakodi]

Hi
I saw that connectionManager constructor  is taking DNSresolver as
parameter . There are two types of DNSresolver namely
SystemDefaultDNSResolver and InMemoryDNSresolver. When does Apache
httpClient uses these class? If my request url has IPinstead of hostname
will this DNSresolver class still be used?Do I get optimization if I load
the InetAddress once and reuse them?

Thanks,
Guru