How can I get Enum fields names using reflection in Java?

Question

This is my class:

public enum Currency {
    NIS, USD, EUR, GBP, JPY, AUD, CAD, DKK, NOK, ZAR, SEK, CHF, JOD, LBP, EGP;

    private String name;
    private int unit;
    private String country;
    private double rate;
    private double change;
}

When I tried to get the fields names of this class using reflection I got the private fields and the enum constants (NIS,EUR,....)

How can I get only the private fields names?

Your fields don't have any values, so why do you want to access them? If you're planning on setting the values through reflection run-time, you might want to reconsider your design. Enums should be compile-time constants. — Mick Mnemonic, May 12 '15 at 18:41
The enum code seems to be incomplete, the constructor and access methods are missing. — MaxZoom, May 12 '15 at 18:43
Get the fields and pick out the ones you want with `Field.getModifiers()`. (Though I suspect you might want every field that isn't an enum constant, rather than just the private fields, so you might want `Field.isEnumConstant()`.) — user2357112, May 12 '15 at 18:45
I want to get the names of the fields. I edited the question — Alex K, May 12 '15 at 19:11

Shar1er80 · Accepted Answer · 2015-05-12T19:30:03.513

UPDATE

From your comment, try the following. It also does not pick up any public fields if you were to have any.

    Field[] allFields = Currency.class.getDeclaredFields();
    for (Field field : allFields) {
        if (Modifier.isPrivate(field.getModifiers())) {
            System.out.println(field.getName());
        }
    }

Results:

enter image description here

To get rid of the $VALUES from the result check if the field is not synthetic

    Field[] allFields = Currency.class.getDeclaredFields();
    for (Field field : allFields) {
        if (Modifier.isPrivate(field.getModifiers()) && !field.isSynthetic()) {
            System.out.println(field.getName());
        }
    }

Results:

enter image description here

As far as giving values to these fields and accessing them you don't need to do reflection to do this. You just need to define the fields appropriately with each enum as followed.

public enum Currency {
    NIS("Name1", 0, "NIS", 1, 2), 
    USD("Name2", 1, "USD", 1, 2), 
    EUR("Name3", 2, "EUR", 1, 2), 
    GBP("Name4", 3, "GBP", 1, 2), 
    JPY("Name5", 4, "JPY", 1, 2), 
    AUD("Name6", 5, "AUD", 1, 2), 
    CAD("Name7", 6, "CAD", 1, 2), 
    DKK("Name8", 7, "DKK", 1, 2), 
    NOK("Name9", 8, "NOK", 1, 2), 
    ZAR("Name10", 9, "ZAR", 1, 2), 
    SEK("Name11", 10, "SEK", 1, 2), 
    CHF("Name12", 11, "CHF", 1, 2), 
    JOD("Name13", 12, "JOD", 1, 2), 
    LBP("Name14", 13, "LBP", 1, 2), 
    EGP("Name15", 14, "EGP", 1, 2);

    private final String name;
    private final int unit;
    private final String country;
    private final double rate;
    private final double change;

    private Currency(String name, int unit, String country, double rate, double change) {
        this.name = name;
        this.unit = unit;
        this.country = country;
        this.rate = rate;
        this.change = change;
    }

    public String getName() {
        return name;
    }

    public int getUnit() {
        return unit;
    }

    public String getCountry() {
        return country;
    }

    public double getRate() {
        return rate;
    }

    public double getChange() {
        return change;
    }
}

The usage of this would be:

public static void main(String[] args) throws Exception {
    for (Currency currency : Currency.values()) {
        System.out.println("Name: " + currency.getName());
        System.out.println("Unit: " + currency.getUnit());
        System.out.println("Country: " + currency.getCountry());
        System.out.println("Rate: " + currency.getRate());
        System.out.println("Change: " + currency.getChange());
        System.out.println("");
    }
}

Results (Not all results are displayed):

enter image description here

Or you can directly use an enum as followed:

System.out.println(Currency.AUD.getName() + " " + Currency.AUD.getCountry());

Result:

Name6 AUD

ZhongYu · Answer 2 · 2015-05-12T19:02:26.220

3

Try test Field.isEnumConstant()

Also you can check getModifiers() and test if it's static, private, etc.

Also isSynthetic() might be needed for testing too.

edited May 12 '15 at 19:02

answered May 12 '15 at 18:56

ZhongYu

19,446
5
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Your answer is better :) – Juan Lopes May 12 '15 at 19:04
@JuanLopes my answer is not complete; you should probably restore and tweak your answer a little bit, so that we have a real answer here. – ZhongYu May 12 '15 at 19:14
@AlexKapustian: [Are you just using us to read the documentation for you? Because if you looked at the documentation, you would see `Field.getName()`.](https://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Field.html#getName--) – user2357112 May 12 '15 at 19:19

Juan Lopes · Answer 3 · 2015-05-12T19:16:29.723

1

This code should do it (based on bayou.io's answer):

List<String> fields = Arrays.stream(Currency.class.getDeclaredFields())
        .filter(x -> !x.isEnumConstant() && !x.isSynthetic())
        .map(x -> x.getName())
        .collect(Collectors.toList());

It just iterates all the fields, filtering the ones that aren't enum constants nor synthetic (like the $VALUES field).

edited May 12 '15 at 19:16

answered May 12 '15 at 18:53

Juan Lopes

10,143
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1

they do have an obscure method in `Field` for that:) I wonder how it's implemented though. – ZhongYu May 12 '15 at 18:57
Yes, but it misses the field "$VALUES". – Juan Lopes May 12 '15 at 19:00
1

use `isSynthetic()` can probably filter it out – ZhongYu May 12 '15 at 19:01
The OP only wants the private field names. This does not work if there are public field names in the enum. – Shar1er80 May 12 '15 at 19:26

How can I get Enum fields names using reflection in Java?

3 Answers3

UPDATE