来源:http://www.blogjava.net/cj78go/archive/2006/09/19/70525.htmlhtml
In asynchronous communication, while the server is listening or receiving data from a client, it can still process connection requests from other clients as well as receive data from those clients. When a server is receiving asynchronously, a separate thread (at the OS level) listens on the socket and will invoke a callback function (specified when the asynchronous listening was commenced) when a socket event occurs. This callback function in turn will respond and process that socket event. For example, if the remote program writes some data to the socket, a "read data event" (callback function you specify) is invoked; it knows how to read the data from the socket at that point.
简而言之,同步是一对一的,异步是一对多的。我翻译的太牛了,这么多英文就让我一句话就归纳了。java