Trying to find class within List

Question

Possible Duplicate:
Get generic type of java.util.List

How can I see what type is within a list in a parameter

private List<String> names;

how would I be able to find out that its a list of Strings? My goal is to make a method like this working:

public Field findFieldByObjectType(Class<?> clazz, Object obj) {
    for (Field field : clazz.getDeclaredFields()) {
        // if field type is List<obj>
        // return field
    }
}

This OS question should give you some clues: http://stackoverflow.com/q/3403909/1916110 — Tom, Jan 13 '13 at 17:48
Do you want the static type (as declared) or the type of the elements in a specific instance? — Henry, Jan 13 '13 at 17:49
This is the closest thing you can achieve http://stackoverflow.com/a/1942680/1317692 — Fallup, Jan 13 '13 at 17:50

score 1 · Answer 1 · answered Jan 13 '13 at 17:47

1

You can either use instanceof operator or the getClass() method on the element(s) of the list.

private List<String> names;

becomes

private List names;

after type erasure.

answered Jan 13 '13 at 17:47

Bhesh Gurung

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But how can I do getClass() on the elements? The list isnt even initialized – Moose Moose Jan 13 '13 at 17:48
The getClass() works at runtime by when you should have it initilized. – Bhesh Gurung Jan 13 '13 at 17:51
@MooseMoose you cannot, since `.getClass()` is a runtime operation, and the generic type is erased at runtime (this is called type erasure). IOW, there is no such thing as `List.class`, at runtime, it becomes `List.class`. – fge Jan 13 '13 at 17:51
No since I'm only getting the fields from the Class>, it will never be initialized – Moose Moose Jan 13 '13 at 17:52
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thats not true, when I'm printing field.getGenericType() it gives me java.util.List – Moose Moose Jan 13 '13 at 17:59

score 1 · Accepted Answer · edited May 23 '17 at 12:18

1

As I said in comments, this is the closest thing what you can achieve with the help of reflection https://stackoverflow.com/a/1942680/1317692. Credit goes to BalusC.

edited May 23 '17 at 12:18

Community

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answered Jan 13 '13 at 18:15

Fallup

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Trying to find class within List

2 Answers2