API Contents - SCJP Sun Certified Programmer for Java Platform SE6 - page 271

Each wrapper class has a “value” method that unwraps the primitive type. For
example, the Float class has a floatValue method that returns the float .
Let's look at an example. The following code wraps an int into an Integer object:
int x = 357;
Integer w = new Integer(x);
The Integer class has a method named intValue that unwraps the int :
int y = w.intValue();
Autoboxing
As of Java 5.0, primitive types can be automatically boxed and unboxed into their
corresponding wrapper classes, eliminating the need for instantiating a new wrapper
type to box a primitive, or using a value method to retrieve the wrapped primitive.
Let's look at an example where a wrapper class is necessary. The following class con-
tains a method named addScore with an Object parameter. Because a primitive type is not
an Object , a primitive type needs to be wrapped before it can be passed into addScore .
Study the following code and try to determine its output:
1. public class ScoreKeeper {
2. public java.util.ArrayList<Object> scores =
3. new java.util.ArrayList<Object>();
4.
5. public void addScore(Object score) {
6. scores.add(score);
7. }
8.
9. public void printScores() {
10. for(Object score : scores) {
11. System.out.println(score);
12. }
13. }
14.
15. public static void main(String [] args) {
16. ScoreKeeper keeper = new ScoreKeeper();
17. Integer one = new Integer(50);
18. Double two = new Double(23.4);
19. Float three = new Float(18.5);
20. keeper.addScore(one);