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What does List<?> mean in java generics?
What does the question mark in Java generics' type parameter mean?
Apologies but it was difficult trying to search for <?>.
What does mean in regards to Java generics? I understand <A extends B> and <A super B>, but I have never seen this question mark on its own before.
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In object-oriented programming, a class is a basic building block. It can be defined as template that describes the data and behaviour associated with the class instantiation.
super T denotes an unknown type that is a supertype of T (or T itself; remember that the supertype relation is reflexive). It is the dual of the bounded wildcards we've been using, where we use ? extends T to denote an unknown type that is a subtype of T .
super is a lower bound, and extends is an upper bound.
T is meant to be a Type. E is meant to be an Element ( List<E> : a list of Elements) K is Key (in a Map<K,V> ) V is Value (as a return value or mapped value)
<?> is a shorthand for <? extends Object>, it's also known as an unbounded wildcard. So you can specify any type of object in your generic.
For example the List class is declared as List<?>, because it can be a list of anything you want.
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