Hi,

I need to convert something, say A1 to b1, B1 to c1, C1 to d1, before
calculation. After calculation is done, I need to convert them back to
its original values, that is b1 to A1, c1 to B1, d1 to C1. It sounds
like I need a two-way mapping Map. Is such a data structure available in
Java?

Of course, I can use two separate Map<String, String>.
First map:
A1-->b1
B1-->c1
C1-->d1

Second map:
b1-->A1
c1-->B1
d1-->C1

I am just curious if there is one Map can do all above.

Another related, but more difficult question is that:

suppose that there are four columns: column A, column B, column C, and
column D. At one time, I need to map from column A to column C. Other
time, I need to map from column A to column B. Sometime I need to map
from column C to column D and from column C to column A. For example,
suppose one row of the four columns are:

"rain", "inch", "precipitation", "mm"

Sometimes, I need to use "rain" as a key to retrieve the column C value,
"precipitation"; sometimes, I need to use "rain" as a key to retrieve
the colunm B value, "inch"; sometimes, I need to use "precipitation" as
a key to retrieve the column A value, "rain"; sometimes, I need to use
"precipitation" as a key to retrieve the colunm D value, "mm".

Is some data structure that allows me do that?

Thank you very much.