— Scott McNealy, Sun Microsystems Chairman, President and ceo

int
giveNumber() { 
return x;
}
if (
bool
) {
System.out.println(“true”);
}
boolean
true
boole
an obje
ct
true

---

292
 
chapter 10
But wait! There’s more! Wrappers
have static utility methods too!
Besides acting like a normal class, the wrappers have a 
bunch of really useful static methods. We’ve used one in 
this book before—Integer.parseInt().
The parse methods take a String and give you back a 
primitive value. 
String s = “2”;
int x = Integer.parseInt(s);
double d = Double.parseDouble(“420.24”);
boolean b = new Boolean(“true”).booleanValue();
Converting a String to a 
primitive value is easy:
No problem to parse 
“2” into 2.
Uh-oh. This compiles just fine, but 
at runtime it blows up. Anything 
that can’t be parsed as a number 
will cause a NumberFormatException
File Edit Window Help Clue
% java Wrappers
Exception in thread “main” 
java.lang.NumberFormatException: two
at java.lang.Integer.parseInt(Integer.java:409)
at java.lang.Integer.parseInt(Integer.java:458)
at Wrappers.main(Wrappers.java:9)
String t = “two”;
int y = Integer.parseInt(t);
But if you try to do this:
You’ll get a runtime exception:
You’d think there would be a 
Boolean.parseBoolean() wouldn’t 
you? But there 
isn’t. Fortunately there’s 
a Boolean constructor 
that takes (and parses) a String, and then you 
just get the primitive value by unwrapping it.
Every method or 
constructor that parses 
a String can throw a 
NumberFormatException. 
It’s a runtime exception, 
so you don’t have to 
handle or declare it.
But you might want to.