How to create a map with enum values in java?

Question

I need to validate the value of a parameters passed as part of REST API. These parameters are a fixed set of values. I thought of using a map having parameter name as key and enum as value. So I can check if the value sent in REST API is one of the enum keys.

But I am not able to create a Map with String key and enum value in java, tried creating Map and then putting and enum as value, but it fails.

class Validation {
    enum Type {
        INTERNAL,
        EXTERNAL
    }; 
}

Map<String, Object> validationMap = new HashMap<String, Object>();
validationMap.put("type", Validation.Type);

This is throwing an error that type is not defined.

What are you actually trying to do? For example Validation.type.class would compile; but does this actually do what you want? — Andy Turner
– Andy Turner, Commented Dec 19, 2018 at 11:30
Make sure you follow the Java Naming Conventions: class and enum names always start with uppercase, i.e. type should be Type. — MC Emperor
– MC Emperor, Commented Dec 19, 2018 at 11:38
Do you need a Map? Will (correcting case) Validation.Type.valueOf() not work? — Tom Hawtin - tackline
– Tom Hawtin - tackline, Commented Dec 19, 2018 at 11:38
@AndyTurner : Validation.type.class solves compilation problem, but I don't know how i can create an instance back using the class. — Pradeep
– Pradeep, Commented Dec 20, 2018 at 11:27

Mark · Accepted Answer · 2018-12-19 11:30:11Z

6

This is probably what you're looking for, Map<String, Object> is changed to Map<String, Validation.type>:

Map<String, Validation.type> validationMap = new HashMap<String, Validation.type>();
validationMap.put("type", Validation.type.INTERNAL);
validationMap.put("type2", Validation.type.EXTERNAL);

Your original code would have worked, if you had changed Validation.type to Validation.type.INTERNAL for example, however your validationMap map allows the storage of any Object, so validationMap.put("type2", 123.123); would also have worked, which is unlikely to be something you want.

answered Dec 19, 2018 at 11:30

Mark

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1 Comment

Pradeep Over a year ago

I like to put enum as value not the properties of enum.

Nicholas K · Accepted Answer · 2018-12-19 14:16:10Z

2

Is this what you need?

Map<String, List<Validation.type>> validationMap = new HashMap<>();
validationMap.put("type", 
   Arrays.asList(Validation.type.EXTERNAL,Validation.type.INTERNAL));

edited Dec 19, 2018 at 14:16

Nicholas K

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answered Dec 19, 2018 at 11:35

TongChen

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Comments

David R. · Accepted Answer · 2022-03-27 02:54:02Z

I believe Your code does not work because Validation.Type is not an instance (of an enum). When you put a value in your map, I believe you would want to put in an actual instance as a value. I suppose that is why the above answers suggest adding an actual instance to the Map such as Type.INTERNAL or using a class instance.

This code will run

    Map<String, Object> validationMap = new HashMap<String, Object>();
    // this works
    validationMap.put("type", Validation.Type.EXTERNAL);
    // as shown by:
    System.out.println(validationMap.toString());
    // here is an analogy:
    // make an instance of a class
    Validation validation = new Validation();
    // this works
    validationMap.put("classType",validation);
    Validation validationGet = (Validation) validationMap.get("classType");
    System.out.println(validationMap.toString());
    // by analogy this will not work because Validation is not an instance:
    // validationMap.put("classType",Validation);

And the output on my machine is: {type=EXTERNAL}

{type=EXTERNAL, classType=Validation@3feba861}

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