API Contents - SCJP Sun Certified Programmer for Java Platform SE6 - page 272

21. keeper.addScore(two);
22. keeper.addScore(three);
23. keeper.printScores();
24. }
25. }
Within main , an int , double , and float are wrapped into their corresponding wrapper
class and passed into the addScore method of a new ScoreKeeper object. The code com-
piles because Integer , Double , and Float are subclasses of Object . Each object is saved in
the ArrayList , and invoking printScores generates the following output:
50
23.4
18.5
Parsing Strings Using the Wrapper Classes
Each wrapper class (except for Character ) contains a useful method for parsing String
objects into primitive types. The name of the method is parse Xxx , where Xxx is the data
type being parsed to. For example, parseInt in the Integer class parses a String to an
int , parseShort in the Short class parses a String to a short , and so on. The following
statements parse a String into a double :
String s = ”123.4”;
double d = Double.parseDouble(s);
double twice = d * 2;
System.out.println(twice);
The String ”123.4” is parsed into a double , multiplied by 2 , and the output is
246.8
Each parse method throws a NumberFormatException if the given String does not
contain a value that is parseable to the appropriate type.
The wrapper classes are used whenever a primitive type needs to be treated as an
Object . Java 5.0 introduced an autoboxing feature that hides the wrapper classes behind
the scenes. The next section discusses autoboxing and unboxing in detail.
Autoboxing and Unboxing
As of Java 5.0, you no longer need to write the code to wrap primitive types into their cor-
responding wrapper class; the compiler now does this for you behind the scenes. The term