getting all static variables in a class into array/list

Question

Bit of a wierd requirement.

public class DummyClass{
   public static final DummyClass var1;
   public static final DummyClass var2;
   public static final DummyClass var3;
    .
    .
    .
   public static final DummyClass var100;
}

Now from outside of this class can we pool this var's into a single array or list, so that I can iterate over them? Like if i do something like

List<DummyClass> dummyList = *some op*; //I want value of some op.

I should be able to access var1...var100

I cannot change the source of DummyClass. – Chandra Dec 17 '10 at 00:36 — Chandra, Dec 17 '10 at 00:36
I would look into using reflection. – Robert Dec 17 '10 at 00:38 — Robert, Dec 17 '10 at 00:38
Can you make it an enum? – Tom Hawtin - tackline Dec 17 '10 at 01:12 — Tom Hawtin - tackline, Dec 17 '10 at 01:12
@Tom As I said, I do not have access to source file. – Chandra Dec 17 '10 at 02:10 — Chandra, Dec 17 '10 at 02:10

Cameron Skinner · Accepted Answer · 2017-07-25T05:14:28.750

47

You could use reflection:

Field[] fields = DummyClass.class.getDeclaredFields();
for (Field f : fields) {
    if (Modifier.isStatic(f.getModifiers()) && isRightName(f.getName())) {
        doWhatever(f);
    } 
}

edited Jul 25 '17 at 05:14

answered Dec 17 '10 at 00:41

Cameron Skinner

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@Chandra Please mark an aswer correct, if you think its correct solution – Ratna Dinakar Dec 17 '10 at 01:07
@Cameron I don't find any isRghtName() method in the Modifier class. – Naruto Uzumaki Jun 06 '13 at 09:38
3

@NarutoUzumaki: It's pseudocode. `isRightName` is meant to signify user code that decides if the field name is interesting. Note that this snippet does not call `Modifier.isRightName`; it's just `isRightName`. – Cameron Skinner Jun 06 '13 at 22:54
Should the `&&` really be inside the `isStatic`-method? If so there are still two `)` missing in the if statement. – jmattheis Jul 24 '17 at 07:35
@CameronSkinner how I can make it to a genenal util method for all this kind of Classes, I tried pass DummyClass as a parameter that argument is a type of class? but not worked. thx. code is something like: `public void printAllProps(Class c) { }` – neifnei Jul 30 '20 at 14:22

score 3 · Answer 2 · answered Sep 28 '19 at 20:31

If you have a class with constants and want to get the actual values of your java constant you can do following:

   List<String> constantValues = Arrays.stream(DummyClass.class.getDeclaredFields())
      .filter(field -> Modifier.isStatic(field.getModifiers()))
      .map(field -> {
        try {
          return (String) field.get(DummyClass.class);
        } catch (IllegalAccessException e) {
          throw new RuntimeException(e);
        }
      })
      .filter(name -> ! name.equals("NOT_NEEDED_CONSTANT") // filter out if needed 
      .collect(Collectors.toList());

getting all static variables in a class into array/list

2 Answers2

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