(The Android chat tool written and implemented in Java uses YQAndroid, a QQ like function, to realize online instant chat. It is divided into client and server. The client and server adhere to the thread of communication and constantly read the data sent by the server. The server should be simpler, only in terms of functions, without beautifying the interface, while the client is relatively messy, sending messages from the server by broadcasting, and updating online friends, including resource files. Comments have been added to the source code, which is helpful for understanding the implementation principle. This document includes the following annexes:)