Primitives as Types - The Java Programming Language - page 283

8.5. Character
The Character class represents the char type as a class. It provides meth-
ods for determining the type of a character (letter, digit, uppercase, and
so forth) and for converting between uppercase and lowercase.
Since a char is a 16-bit value, and Unicode allows for 21-bit characters,
known as code points, many of the methods of Character are overloaded
to take either a char or an int that represents an arbitrary code point.
Such methods are described in combination below and the pseudo-type
codePoint is used to represent either a char or an int code point value.
In addition to MIN_VALUE and MAX_VALUE constants, Character provides the
constants MIN_RADIX and MAX_RADIX , which are the minimum and maximum
radices understood by methods that translate between digit characters
and integer values or vice versa,. The radix must be in the range 236;
digits for values greater than 9 are the letters A tHRough Z or their lower-
case equivalents. Three methods convert between characters and integer
values:
public static int digit( codePoint ch, int radix)
Returns the numeric value of ch considered as a digit in the
given radix. If the radix is not valid or if ch is not a digit in the
radix, 1 is returned. For example, digit('A',16) returns 10 and
digit('9',10) returns 9, while digit('a',10) returns 1.
public static int getNumericValue( codePoint ch)
Returns the numeric value of the digit ch . For example, the
character \u217F is the Roman numeral digit M , so getNumer-
icValue('\u217F') returns the value 1000. These numeric val-
ues are non-negative. If ch has no numeric value, 1 is re-
turned; if it has a value but is not a non-negative integer, such
as the fractional value ¼ ( '\u00bc' ), getNumericValue returns 2.