Question

What is the proper Java type to use for a lookup table of constants that have a one-to-one relationship with other constants? For instance:

A1 <-> B1
A2 <-> B2
A3 <-> B3

where all As and Bs are known at compile time. I need to be able to call something like this in the code:

B = getB(A)

My initial thoughts were a Map or Enum.

Answer 1

If you just want the mapping to go one way (i.e. lookup B for A), then a java.util.Map implementation will do fine.

If you want the mapping to go both ways (i.e. lookup B for A and lookup A for B), then either use two java.util.Map instances or a bidirectional map interface; e.g. the Guava BiMap interface.