What are generics?

they let you pass type as a parameter. The most simple instance is something like ArrayList. Being able to set the type lets you have an arrayList of Strings (ArrayList<String>), or an ArrayList of Dates(ArrayList<Date>). They typically contrast this with raw type (accepts any object). You could pass any of a series of objects into an arraylist of objects, but you wouldn't get type protection (during compile) and you'd need to do more casting. Such code would be brittle as passing in an incorrect object type would fail during runtime when casting. (for the record, most explanations of generics delve into an explanation of type issues with raw type - which is pregeneric behaviour. generics are confusing until you see how they used to code before generics were introduced. see https://docs.oracle.com/javase/tutorial/java/generics/why.html )

Moderator Edit: Moved response to Answer section