An instance of an InetAddress consists of an IP address and possibly its corresponding host name (depending on whether it is constructed with a host name or whether it has already done reverse host name resolution).
When four parts are specified, each is interpreted as a byte of data and assigned, from left to right, to the four bytes of an IPv4 address. When a three part address is specified, the last part is interpreted as a 16-bit quantity and placed in the right most two bytes of the network address. This makes the three part address format convenient for specifying Class B net- work addresses as 128.net.host. When a two part address is supplied, the last part is interpreted as a 24-bit quantity and placed in the right most three bytes of the network address. This makes the two part address format convenient for specifying Class A network addresses as net.host. When only one part is given, the value is stored directly in the network address without any byte rearrangement. For methods that return a textual representation as output value, the first form, i.e. a dotted-quad string, is used.
对ipv4就是个32位的二进制而已，不就想通了