Question

mDualPane = detailsFrame != null && detailsFrame.getVisibility() == View.VISIBLE;

what are the meaning of this line?
why there are those many = ?

Answer 1

It would be easier to understand if it was written like this:

mDualPane = ((detailsFrame != null) && 
             (detailsFrame.getVisibility() == View.VISIBLE));

Which breaks it into a single boolean value which is returned from the AND (&&) of the two conditions above:

detailsFrame != null

And

detailsFrame.getVisibility() == View.VISIBLE

We first check that detailsFrame != null in order to avoid NPE – only then we check that it’s visible by calling: detailsFrame.getVisibility()