android launch apk,App launch in android

We can launch the app in two ways, 1 is form the app, clicking on device back button till we reach the android home screen and launching the app or 2nd is from the app we can click the device home button and then we can launch.

How can we differentiate these to launches? In 2nd type launch onrestart will be called, onrestart will be called in some other cases also.

I want to do something in the 2nd type of launch.

Can any one tel me how to do this...

Thanks in advance.