Java getConstructor(types) with parametised types

Question

If I have a class with a constructor that takes a parametized generic type:

public class Foo {
    public Foo(Map<String, Object> data) {
      ...
    }
}

... how do I reference that parametized Map's class if I want to call:

Constructor constructor = cls.getConstructor(/*the Map class! */)

(Where cls is the Foo class.)

I want to do something like:

Constructor constructor = cls.getConstructor(Map<String,Object>.class);

... but that doesn't work.

I'm sure there's a simple answer to this!

Check out this link on Java "type erasure". See also Reflecting generic types. — paulsm4
– paulsm4, Commented Aug 23, 2012 at 22:41
Ah yes type erasure, had I thought more about this and actually read what Eclipse was trying to tell me I probably would have figured that out! Anyway, thanks for the link. — Mikesname
– Mikesname, Commented Aug 23, 2012 at 22:45

John Ericksen · Accepted Answer · 2012-08-24 03:06:31Z

14

At runtime, this:

  Map<String,Object>

Is actually just a Map, without any parameters.

Calling

 cls.getConstructor(Map.class) will be enough

John Ericksen

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answered Aug 23, 2012 at 22:38

Eugene

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Comments

John Ericksen · Accepted Answer · 2012-08-23 22:39:40Z

4

You can reference the constructor by just the Map type. The generic parameters are erased for runtime:

Constructor constructor = Foo.class.getConstructor(Map.class);

answered Aug 23, 2012 at 22:39

John Ericksen

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