I see an unfamiliar notation in the Android source code: *=
*=
For example: density *= invertedRatio;
density *= invertedRatio;
I am not familiar with the star-
Just like Da said, it's short for density = density * invertedRatio; - it's nothing Android specific, it's standard Java. You will find this (and similar operators) in many languages with a C-like syntax.
density = density * invertedRatio;