The key concepts of Java Generics are easy to grasp: parameterize a type with a type variable, et voilà, the result is a generic type. Likewise for generic methods. An example of a generic type is the generic interface List<E> {...} which can be used to form parameterized types such as List<String> or List<Double> , but also List<? extends Number> , which involves use of a wildcard.  Wildcards are probably the most difficult-to-grasp element of Java Generics. Yet, they are everything but syntactic sugar.  Quite the converse, they are frequently needed as argument types of carefully crafted methods. An example is <T> void sort(List<T> list,Comparator<? super T> c) in class java.util.Collections .  The " ? super T "-wildcard is needed, because the method would otherwise mistakenly prevent sorting a List<Double> with a Comparator<Number> .

In this session we will give a brief recap of the key concepts of Java Generics and all involved syntax elements. Then we, as a mob, will program using Java generics.  The idea is the following: the presenter sets up a programming task, the attendants suggest the source code, the presenter types it in, and then we'll see what happens.  It's a unique opportunity to learn everything you always wanted to know about generics (but were afraid to ask) and to step into every known pitfall (that a novice to generics typically steps into).