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javagenericsenums
icvg
icvg

Reputation: 197

Java Enums values with Generics

I need something like this:

public enum Enum {
    ENUM1<Class1>(Class1.class, "A DESCRIPTION", new Class1()),
    ENUM2<Class2>(Class2.class, "A DESCRIPTION", new Class2()),
    ENUM3<Class3>(Class3.class, "A DESCRIPTION", new Class3());

    private Enum(Class<? extends Object> clazz, String description, Object instance) {}
}

What I need: a single place where I define different instances of all ClassX (they extend the same ClassSuper). Of course I could define different Enums for every ClassX, but this is not really what I want.

Upvotes: 6

Views: 575

Answers (3)

Peter Lawrey
Peter Lawrey

Reputation: 533492

You can write the following to hold all the same information (as the class can be obtained from the class)

public enum Enum {
    ENUM1("A DESCRIPTION", new Class1()),
    ENUM2("A DESCRIPTION", new Class2()),
    ENUM3("A DESCRIPTION", new Class3());

    private Enum(String description, Object instance) {}
}

The problem you will find is that with enums, generics are not as useful and you can write much the same behaviour without generics.

Upvotes: 1

dcernahoschi
dcernahoschi

Reputation: 15230

JLS does not allow type parameters for an enum:

EnumDeclaration:
    ClassModifiers(opt) enum Identifier Interfaces(opt) EnumBody

EnumBody:
    { EnumConstants(opt) ,(opt) EnumBodyDeclarations(opt) }

Upvotes: 6

Alex Coleman
Alex Coleman

Reputation: 7326

Enum's can in fact have fields, and it looks like that is what you want:

private Object instance;
private Enum(Class<? extends Object> clazz, String description, Object instance) {
    this.instance=instance;
}
public Object getInstance() {
    return instance;
}

As far as I can tell, enums cant be paramitized though, so you cant have that in your code. What exactly are you trying to do with these classes though? I may be misunderstanding your question

Upvotes: 1

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