What are wildcards in Java and can you provide some examples?

What are wildcards in Java and can you provide some examples?

Wildcards in Java are used in generics to represent an unknown type. They are denoted by the question mark (?). For example, List<?> can hold a list of any type.

Can you explain the different types of wildcards?

Sure! There are three types of wildcards: unbounded (?), upper-bounded (<? extends T>), and lower-bounded (<? super T>). Unbounded wildcards can represent any type, upper-bounded wildcards restrict the unknown type to be a subtype of a specified type, and lower-bounded wildcards restrict it to be a supertype.

Could you give me a code example for each type?

Absolutely! Here are examples:

1. Unbounded: List<?> list = new ArrayList<String>();
2. Upper-bounded: List<? extends Number> numberList = new ArrayList<Integer>();
3. Lower-bounded: List<? super Integer> integerList = new ArrayList<Number>();

How do wildcards improve code flexibility?

Wildcards allow for more flexible and reusable code by enabling methods to accept a wider range of types, making it easier to work with collections.