Wrappers with null
Unlike primitives, a wrapper variable can be uninitialized and has a value of null. A primitive variable that is not initialized is automatically set to its default value (0 in the case of ints). Since wrappers can have null values, this allows us to test if it has been set before using it (unlike primitives). In this exercise, we see the difference between uninitialized primitives and wrapper objects.
Deze oefening maakt deel uit van de cursus
Data Types and Exceptions in Java
Oefeninstructies
- Declare a variable of type
intcalledxbut do not set its value. - Declare a variable of type
Integercalledybut do not set its value. - Display (print) the value of
xeven though you did not initialize its value. - Test if
yisnull.
Praktische interactieve oefening
Probeer deze oefening eens door deze voorbeeldcode in te vullen.
public class NullWithWrappers {
// Declare a primitive integer called x
static ____ ____;
// Declare a wrapper Integer called y
static ____ ____;
public static void main(String[] args) {
// Display x value
System.out.____(____);
System.out.println(y);
// Check if y has been initialized and is null
if (____ ____ ____) {
System.out.println("y is not initialized so take corrective steps here");
}
}
}