-
Notifications
You must be signed in to change notification settings - Fork 17
Java Generics Upper Bounded Wildcards Example
Ramesh Fadatare edited this page Aug 19, 2018
·
1 revision
To specify an upper bound for wildcards, use this syntax,
GenericType<? extends SuperClass>This specifies that a wildcard argument can contain ‘SuperClass’ type or it subclasses. Remember that extends clause is an inclusive bound. i.e ‘SuperClass’ also lies in the bound.
In the above example, if you want the processElements() method to work with only numbers, then you can specify an upper bound for wildcard argument.
import java.util.ArrayList;
import java.util.List;
/**
* Wildcard Arguments With An Upper Bound Demo
* @author javaguides.net
*
*/
public class WildCardWithUpperBoundExample {
static void processElements(List<? extends Number> a) {
for (Object element : a) {
System.out.println(element);
}
}
public static void main(String[] args) {
// ArrayList Containing Integers
List<Integer> a1 = new ArrayList<>();
a1.add(10);
a1.add(20);
a1.add(30);
processElements(a1);
// ArrayList Containing Longs
List<Long> a2 = new ArrayList<>();
a2.add(100L);
a2.add(200L);
a2.add(300L);
processElements(a2);
// Arraylist containing Doubles
List<Double> a3 = new ArrayList<>();
a3.add(21.35);
a3.add(56.47);
a3.add(78.12);
processElements(a3);
// Arraylist containing Strings
List<String> a4 = new ArrayList<>();
a4.add("One");
a4.add("Two");
a4.add("Three");
// This will not work
//processElements(a4); // Compile time error
}
}Output:
10
20
30
10
20
30
21.35
56.47
78.12