List all constants of specified class

Question

My question is: how to create a list of all constants of specified class?

Is this possible in an easy way? Or I just need to write my own (somewhat simple) solution for this?

Let me present some code:

public class StateOfSomeProcess {
    private final static String STATE_A = "State A";
    private final static String STATE_B = "State B";
    private final static String STATE_C = "State C";
    private final static String STATE_D = "State D";

    public StateOfSomeProcess() {...}

    public List<String> getListOfAllStates() {
        List<String> list = new ArrayList<String>();
        ...
        //I wish there was a method like this:
        //list = this.getAllConstantsFromClass();
        ...
        return list;
    }
}

I know about enums, but it does not seem to fit my needs. Please feel free to let me know if my question is unclear or needs improvement.

Are you familiar with the concept of "reflection"? http://docs.oracle.com/javase/tutorial/reflect/ — Jeroen Vannevel, Nov 02 '14 at 23:09
reflection will do it the nice way. also, you could add all those constants to a static array: private static String[] array = new String[]{STATE_A,STATE_B,STATE_C,STATE_D}; — Michael, Nov 02 '14 at 23:11
Sadly, no, I have never heard about reflection, but I will check it. I am beginner to Java. Thanks for help:) — bercik, Nov 02 '14 at 23:13
IMHO marking the question as a duplicate and downvoting it, is a bit harsh. Especially considering the quality (high) and the experience (low) of the OP. The given link to [Enums VS Classes VS Interfaces](http://stackoverflow.com/questions/6144227) doesn't even provide an answer to the question. — Hille, Nov 02 '14 at 23:53
Thanks, Hille. To others: quote explicitly where is the answer for my question at that 'duplicate question'. I have seen that 5 times, then asked. I suggest you read again what I look for. — bercik, Nov 03 '14 at 12:10

score 6 · Accepted Answer · answered Nov 16 '14 at 14:09

6

You may write

private static List<String> getListOfAllStates() {
    List<String> list = new ArrayList<String>();

    for (Field field : StateOfSomeProcess.class.getDeclaredFields()) {
        int modifiers = field.getModifiers(); 
        if( Modifier.isStatic(modifiers) && Modifier.isFinal(modifiers) ) {
            list.add(field.getName());
        }
    } 
    return list;
}

answered Nov 16 '14 at 14:09

Hille

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Wow! It works like a charm! I have tested it in a small app. But I am also aware of previous answers and the fact that the reflection should be avoided. I think I can write two other solutions that were pointed out by Jeanne Boyarsky. Thanks Hille! – bercik Nov 16 '14 at 23:47

score 1 · Answer 2 · answered Nov 02 '14 at 23:24

I see three options.

Option 1 - create an ArrayList or array yourself

Pros: Fast and easy to do Cons: Easy to get out of date

Option 2 - Use reflection

Pros: It will always be up to date Cons: Slower to run (highly unlikely to be a problem if you only do it once), harder to read the code

Option 3 - Read the file as a string

Pros: It will also be up to date. Cons: Gives you strings, but not Java references. I sometimes use this approach when writing unit tests (for example to confirm I didn't forget to add something manually using approach #1)

Although you didn't provide code example solutions, I must admit that I appreciate your answer. It gives some clues to interesting things to check. Maybe I will use one of them temporarily. Upvote for you! — bercik, Nov 03 '14 at 11:59

score 0 · Answer 3 · answered Apr 13 '21 at 16:06

It's not exactly what was asked but as I had to get a Map of <Constant, Value> I've modified a bit the Jeanne answer and it may help someone:

public class AnyNamesConstants {
    public static final String CONST_1 = "Constant 1";
    
    public static final String CONST_2 = "Constant 2";
    
    public static Map<String, Object> getMapConstValue() throws IllegalAccessException {
    
        Map<String, Object> map = new HashMap<>();
    
        for (Field field : AnyNamesConstants.class.getDeclaredFields()) {
            int modifiers = field.getModifiers();
            if( Modifier.isStatic(modifiers) && Modifier.isFinal(modifiers) ) {
                list.put(field.getName(), field.get(field.getType()));
            }
        }
        return map;
    }
}

You'd get:

{
    "CONST_1": "Constant 1",
    "CONST_2": "Constant 2"
}

List all constants of specified class

3 Answers3