Seven OSI model:
application layer
presentation layer
session layer
transport layer,
network layer,
data link layer,
physical layer
TCP / IP four-layer model
application layer
transport layer
network interconnection layer
network interface layer
Port: means for application interaction channel data, used to implement communications between programs. Each application has a fixed port.
tel telnet protocol port 23
Simple Mail Transfer Protocol smtp port 25
file transfer protocol ftp port 21,
Hypertext Transfer Protocol http port 80
html: HTML. And a sub-tag to tag web content described language. Hypertext is the meaning, not just text data described in html, you can also tag links through a series of a variety of network resources (images, audio, video, css, js). Kefuduan when accessing html page, you need to download not only text data, but also need to issue n multiple requests, the Web page links to resources eleven download
volatile and static variables is a key attribute for modification, modification of the properties of volatile and static variables have the following characteristics:
after 1, when multiple threads access the variable in one thread changes the value of this thread, other threads immediately visible.
2, prohibition instruction rearranged