Java - Generics with lists

Question

I wrote a function for my cache to retrieve a specific object. This way I don't need to cast it .

@SuppressWarnings("unchecked")
    public static <T> T inCache(Class<T> obj, String token) {

        Object cacheObj = Cache.get(token);
        if (cacheObj != null) {

            if (obj.isAssignableFrom(cacheObj.getClass())) {
                return (T) cacheObj;
            }
        }
        return null;

    }

I am using it like this

String s = inCache(String.class, title);

But now I have a list of Strings in my cache and I can't use it like this

List<String> ipList = Util.inCache(List<String>.class, title);

The problem is the List<String>.class . I am very new to java, how do I have to write it?

Answer 1

There is a concept in java called type erasure. Due to legacy reasons, something like List is just a list. It doesn't remember that it is a list of string at run time. You should just write List.class.

You can then specify the type of object in the List when iterating through it.

Answer 2

You can't get class of List<String>, in your case the only way is:

List<String> ipList = (List<String>)Util.inCache(List.class, title);