Java APIs

Just started with Java generics and I am little confused. I read the tutorial but there are still some things I don't get.

The following code works (no surprise there):

	TypeVariable<Class<String>>[] foo = 
	                String.class.getTypeParameters();

but when I do the following:

	
        Class<? extends String> foo = "".getClass();
        TypeVariable<Class<? extends String>>[] bar = foo.getTypeParameters()

I get :

incompatible types
found   : java.lang.reflect.TypeVariable<java.lang.Class<capture of ? extends java.lang.String>>[]
required: java.lang.reflect.TypeVariable<java.lang.Class<? extends java.lang.String>>[]

I can get it to work with wildcards (TypeVariables<?> bar = ...) but I would like to know that this "capture of ? extends String" actually means. And what syntax should be used.

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Magnus