How do you use bounded wildcards (? extends / ? super) with a simple code example?

In Java, bounded wildcards allow you to specify a range of types that can be used in a generic class or method. The two main types of bounded wildcards are ? extends T and ? super T. These can be particularly useful when you're working with collections.

Using `? extends` Wildcard

The ? extends wildcard is used when you want to refer to an unknown subtype of a specific type. This is particularly useful for getting items from a structure, as it allows you to define a read-only access for the collection.

Example:


        // Example: Using ? extends
        import java.util.ArrayList;
        import java.util.List;

        public class BoundedWildcardExample {
            public static void printList(List extends Number> list) {
                for (Number num : list) {
                    System.out.println(num);
                }
            }

            public static void main(String[] args) {
                List integerList = new ArrayList<>();
                integerList.add(1);
                integerList.add(2);
                printList(integerList);  // Accepts List of Integer
            }
        }

Using `? super` Wildcard

The ? super wildcard is used when you want to refer to an unknown supertype of a specific type. This is useful when you want to write items into a structure, as it allows you to provide a write access for the collection.

Example:


        // Example: Using ? super
        import java.util.ArrayList;
        import java.util.List;

        public class BoundedWildcardExample {
            public static void addNumbers(List super Integer> list) {
                list.add(1);
                list.add(2);
            }

            public static void main(String[] args) {
                List numberList = new ArrayList<>();
                addNumbers(numberList);  // Accepts List of Number
            }
        }

How do you use bounded wildcards (? extends / ? super) with a simple code example?

Using `? extends` Wildcard

Example:

Using `? super` Wildcard

Example:

Popular Topics

Recent Languages

How do you use bounded wildcards (? extends / ? super) with a simple code example?

Using ? extends Wildcard

Example:

Using ? super Wildcard

Example:

Related Questions

Popular Topics

Recent Languages

Using `? extends` Wildcard

Using `? super` Wildcard