Get Values from Enum dynamically at Runtime

Question

My enum types-

public enum Foo {A, B, C}

And

public enum Bar {A("aaa"), B("bbb"), C("ccc")}

All I have at runtime is the enum class name i.e. "Foo"

I do this -

Class<?> c = Class.forName(getClassName()) // local function

Using Arrays.asList(c.getEnumConstants()) gets me -

Foo -

[A, B, C]

Bar -

[aaa, bbb, ccc]

I also want [A, B, C] when evaluating Bar.

.values() is what I want but how do I get to it dynamically without any explicit casting?

Many thanks for any replies.

Have found the solution -

List<? extends Enum<?>> enums = (List<? extends Enum<?>>) Arrays.asList(c.getEnumConstants());
for (Enum<?> e: enums) {
    System.err.println("e.name: " + e.name());
}

You should post your own solution as an answer, not as a part of the question. — JavaNewbie_M107
– JavaNewbie_M107, Commented Aug 15, 2013 at 14:20

OldCurmudgeon · Accepted Answer · 2013-08-15 12:23:07Z

3

I suspect your Arrays.asList(c.getEnumConstants()) is actually working correctly. What you are seeing when you print the array out is a list of the toString() results of Bar which become [aaa, bbb, ccc].

Try something like:

for (Bar b : Bar.class.getEnumConstants()) {
  System.out.println(b.name() + "(\"" + b.toString() + "\")");
}

You should see what I mean.

If you have an enum that defines its own toString() you could try wrapping it:

static class EnumNamer<T extends Enum<T>> {
  final T he;

  public EnumNamer(T he) {
    this.he = he;
  }

  @Override
  public String toString() {
    return he.name();
  }
}

public void test() {
  System.out.println("Hello");
  for (Bar b : Bar.class.getEnumConstants()) {
    System.out.println(b.name() + "(\"" + b.toString() + "\")");
    EnumNamer<Bar> en = new EnumNamer<>(b);
    System.out.println(en + "(\"" + en.toString() + "\")");
  }
}

Now you've clarified a few points - this works for me:

// This cast should be OK so long as we KNOW its an enum.
Class<Enum> c = (Class<Enum>)Class.forName(Bar.class.getName());
for (Enum e : c.getEnumConstants()) {
  EnumNamer en = new EnumNamer(e);
  System.out.println(en + "(\"" + en.toString() + "\")");
}

edited Aug 15, 2013 at 12:23

answered Aug 15, 2013 at 11:21

OldCurmudgeon

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4 Comments

Hallam Over a year ago

Ah, yes it does override toString. The question is, how do I get round this without altering the enum?

OldCurmudgeon Over a year ago

Get around what? Perhaps don't call toString(). Perhaps call .name() instead.

Hallam Over a year ago

'.name()' is not available off of 'getEnumConstants()' and as I stated, I cannot do any explicit casting...

OldCurmudgeon Over a year ago

.name() is available from getEnumConstants. See my sample code System.out.println(b.name() ....

Mac · Accepted Answer · 2013-08-15 12:04:52Z

0

For Bar You can use the following code while retrieving the constants:

List<Bar> list = Arrays.asList(c.getEnumConstants());
List<String> list1 = new ArrayList<String>();
for (Bar b : list)
{
   list1.add(b.name());
}
System.out.println(list1);

edited Aug 15, 2013 at 12:04

answered Aug 15, 2013 at 11:58

Mac

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1 Comment

Mac Over a year ago

@OldCurmudgeon: In that case OP can use .name() method of Enum as I have done in my updated code..

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