Lets start with a bit of background: What happens when you start an application?
The OS starts a process and assigns it a unique process id and allocates a process table.A process start an instance of DVM(Dalvik VM); Each application runs inside a DVM.
A DVM manages class loading unloading, instance lifecycle, GC etc.

Lifetime of a static variable: A static variable comes into existence when a class is loaded by the JVM and dies when the class is unloaded.

So if you create an android application and initialize a static variable, it will remain in the JVM until one of the following happens:
1. the class is unloaded
2. the JVM shuts down
3. the process dies

Note that the value of the static variable will persist when you switch to a different activity of another application and none of the above three happens. Should any of the above three happen the static will lose its value.

You can test this with a few lines of code:

  1. print the uninitialized static in onCreate of your activity -> should print null
  2. initialize the static. print it -> value would be non null
  3. Hit the back button and go to home screen. Note: Home screen is another activity.
  4. Launch your activity again -> the static variable will be non-null
  5. Kill your application process from DDMS(stop button in the devices window).
  6. Restart your activity -> the static will have null value.

Hope that helps.