Can you explain wildcards in Java generics?

Can you explain wildcards in Java generics?

Sure! Wildcards in Java generics are represented by the question mark (?) and are used to denote an unknown type. They allow for more flexible code.

What are the different types of wildcards?

There are three types of wildcards: unbounded wildcards (?), upper-bounded wildcards (extends), and lower-bounded wildcards (super). Each serves a different purpose.

Can you give an example of upper-bounded wildcards?

Certainly! An upper-bounded wildcard is defined like this: <? extends Number>. It means that the type can be any subclass of Number, such as Integer or Double.

What about lower-bounded wildcards?

Lower-bounded wildcards are defined using <? super T>, where T is a specific type. This allows you to pass in T or any of its superclasses.

Why should I use wildcards instead of concrete types?

Using wildcards increases the flexibility of your code, allowing for more generic methods and classes that can work with a wider range of types.