Java generic class as parameter

Question

I have a basic question regarding Java generics. I have a method that takes this as an argument:

public id findKey(List<String> ids, CustomClass clazz) {
    repos.findID(ids, clazz);
}

I then want to use a java generic class as an argument for another method:

repos.findID(ids, clazz);

but my findID method needs a java generic class instead of clazz. How do I get my clazz argument from the findkey parameter and turn it to a generic class? If I do this:

public id findKey(List<String> ids, Class<T> clazz) {
    repos.findID(ids, clazz);
}

I get an error because it won't recognize my T.

I'm at loss at how this stuff works and would appreciate any help.

Edit: Solved it. I can use ? or explicitly state a class type that I wanted and it accepted it.

Unless you actually need T elsewhere in your method, Class<?> is sufficient. Otherwise, just define a type variable: public <T> id findKey(.... — Andy Turner
– Andy Turner, Commented Feb 15, 2017 at 12:20
then please answer it yourself - maybe it helps someone else — user85421
– user85421, Commented Feb 15, 2017 at 12:22

Andy Turner · Accepted Answer · 2017-02-15 12:24:01Z

1

There are two options:

define your type as unknown

public id findKey(List<String> ids, Class<?> clazz)

define a type variable

public <T> id findKey(List<String> ids, Class<T> clazz)

edited Feb 15, 2017 at 12:24

Andy Turner

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answered Feb 15, 2017 at 12:23

Martin Strejc

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Michael Kazarian · Accepted Answer · 2017-02-15 12:29:17Z

1

Use public id findKey(List<String> ids, Class<?> clazz) and read more about wildcards

answered Feb 15, 2017 at 12:29

Michael Kazarian

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