I am writing a simulation that will use a set of variables which I plan to
store externally from the code. Default values for the variables will be
stored in a properties file (File 1). For example:

File 1:
X=3
Y=7
Z=2

File 2:
Y=5

After opening and reading File 1, how could I open a SECOND properties file
(File 2) and read values to override the values read from File 1? I want
the end result to be:

X=3
Y=5
Z=2