Defining Classes - Beginning Java - page 245

Converting between Primitive Type Values and Strings
Each class provides a static toString() method to convert a value of the corresponding primitive type to
a String object, as you saw in the last chapter. There is also a non-static toString() method in each class
that returns a String representation of a class object.
Conversely, there are methods to convert from a String object to a primitive type. For example, the
static parseInt() member in the Integer class accepts a String representation of an integer as an argu-
ment and returns the equivalent value as type int . An alternative version of this method accepts a second
argument of type int that specifies the radix to be used when interpreting the string. This enables you to
parse strings that are hexadecimal or octal values, for example. If the String object cannot be parsed for
any reason, if it contains invalid characters, for example, the method throws an exception of type Num-
berFormatException . All the standard classes encapsulating numerical primitive types and the Boolean
class define static methods to parse strings and return a value of the corresponding primitive type. You have
the methods parseShort() , parseByte() , parseInt() , and parseLong() in the classes for integer types,
parseFloat() and parseDouble() for floating-point classes, and parseBoolean() for Boolean .
The classes for primitive numerical types and the Boolean class defines a static method valueOf() that
converts a string to an object of the class type containing the value represented by the string. If the string
does not represent a valid value, NumberFormatException is thrown. The method for the Boolean class
returns a Boolean object with the value true if the string is equal to true ignoring case. Any other string
results in false being returned.
WARNING At the time of writing, the methods, such as parseInt() , for converting strings
to numerical values throw an exception of type NumberFormatException if the string to be
parsed contains underline characters, even though underlines are legal in numerical literals.
This is regarded as a bug so it may well be fixed by the time you are reading this. If not, you
can always write a method to remove underlines from any string that is to be converted to a
numerical value.
Converting Objects to Values
Each class encapsulating a primitive data value also defines a xxxValue() method (where xxx is the cor-
responding primitive type name) that returns the value that is encapsulated by an object as a value of the
corresponding primitive type. For example, if you have created an object number of type Double that encap-
sulates the value 1.14159, then the expression number.doubleValue() results in the value 1.14159 as type
double .
Primitive Class Constants
The classes that wrap numerical primitive types each contain the static final constants MAX_VALUE
and MIN_VALUE that define the maximum and minimum values that can be represented. The floating-point
classes also define the constants POSITIVE_INFINITY , NEGATIVE_INFINITY , and NaN (it stands for N ot a
N umber, as it is the result of 0/0), so you can use these in comparisons to test whether such values have
arisen during calculations. Alternatively, you can test floating-point values with the static methods isIn-