There are similarities in web and android development.
1) file structure is important.
2) XML and java (android APIs) are used.
3)
IDE is similar.
There are differences
1) Java is a little different from java SE. However previous java knowledge is a big plus.
2) The devices that run are very different from web servers. Smaller devices yet ever improving in hardware.
3) User experience and UI is very different from web applications.
It takes around 6 months and useful book/books for the average java/java2ee developer to get a good grasp of android.