What are wildcards in Java generics?

What are wildcards in Java generics?

Wildcards in Java generics are special types that allow you to specify a range of types. They are represented by the '?' symbol.

Can you explain the different types of wildcards?

Sure! There are three types of wildcards: unbounded wildcards (?), upper-bounded wildcards (? extends T), and lower-bounded wildcards (? super T).

When should I use each type of wildcard?

Use unbounded wildcards when you don't care about the type. Use upper-bounded wildcards when you want to read items of a specific type, and lower-bounded wildcards when you want to write items.

Can you give me an example of upper-bounded wildcards?

Certainly! If you have a method that accepts a List<? extends Number>, it can accept a List<Integer>, List<Double>, etc.