Use static final unmodifiable Set as constant for checking variables value
coding-style, java
Solution
Overall, I think this is very good style.
There's not a huge difference, but I'd personally define `SET_OF_CONSTANTS` like so:
public final static String CONSTANT_1 = "*value*";
public final static String CONSTANT_2 = "*value*";
...
public final static String CONSTANT_N = "*value*";
public final static Set<String> SET_OF_CONSTANTS = Collections.unmodifiableSet(
new HashSet<String>(Arrays.asList(
CONSTANT_1,
CONSTANT_2,
...
CONSTANT_N
)));
It's not entirely clear to me whether you even need the separate `CONSTANT_1` constants, or whether you can simply fold the values into `SET_OF_CONSTANTS`.
As far as performance goes, I would not start optimizing anything until I've profiled the code on real data.
Finally, note that when `x` is a string, the following is probably incorrect:
IF x == CONSTANT_1 || x == CONSTANT_2 || ... || x == CONSTANT_N
Here, the `==` should probably be replaced with calls to `equals()`.
Problem
I've often run through a validation pattern where, to be valid, some variables must contain one of a prefixed number of values. ``` PSEUDO CODE: IF x == CONSTANT_1 || X == CONSTANT_2 || ... || x == CONSTANT_N THEN X is valid ``` In order to avoid the chain of OR terms, I created a static final unmodifiable set, which contains all the constants: ``` public final static String CONSTANT_1 = *value* ; public final static String CONSTANT_2 = *value* ; ... public final static String CONSTANT_N = *value* ; public final static Set SET_OF_CONSTANTS = Collections.unmodifiableSet(new HashSet(){ private static final long serialVersionUID = 1L; { add(CONSTANT_1); add(CONSTANT_2); ... add(CONSTANT_3); } }); ``` And I perform the check in the following way: ``` if(!SET_OF_CONSTANTS.contains(x)){ //X NOT VALID } ``` I'd like to know if this is a good programming practice, if there are any alternatives, and if it's true that using a Hash Table query (O(1) in theory) instead of the OR terms-chain improves performance and maybe also code-readability.