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Data Types and Operators :

Variable Type Helper Objects

So far, the variable types we have discussed are called "primitive types" because they represent simple values that have built-in characteristics. They are fixed elements. Java also provides a set of "reference types" that include object arrays, strings, and other more complex data structures.

We'll talk more about reference types later when we are using them. However, it is good to note that Java provides reference "wrapper" types for each primitive type that include manipulative functionality.

These classes can all be found in java.lang and include: Boolean, Character, Double, Float, Integer, Long, and String.

Each class contains helper methods that allow you to more easily work with the values. One of the most useful features provided by the wrapper classes is the ability to easily change from one type to another. Thus, you can change an integer value to its string representation using something like:

     Integer(20).toString();

Consider the list of methods in the following objects:

Boolean
final static Boolean FALSE	Creates a Boolean with a false value
final static Boolean MAX_VALUE	Returns 65535 (this was placed in the boolean class by mistake)
final static Boolean MIN_VALUE	returns 0 (this was placed in the boolean class by mistake)
final static Boolean TRUE	Creates a Boolean with a true value
Boolean(String s)	Creates a Boolean based on the string. true is true. Everything else is false.
Boolean (boolean value)	Creates a Boolean with specified boolean value
boolean booleanValue()	returns the boolean value of the Boolean object
boolean equals(Object object)	Returns true if the objects are equal, false if not.
static boolean getBoolean(String s)	Returns true if s is true. Otherwise it returns false.
int hashCode()	Returns the Boolean's hash code.
String toString()	Returns the string representation of the Boolean.
static Boolean valueOf(String s)	Returns a Boolean representation of the string
Character
final static int MAX_RASIX	The maximum radix that can be used in converting a number to an int (represented as a character). The value is 36.
final static int MIN RADIX	Same as above but returns 2
Character (char value)	Returns a Character representation of value.
char charValue()	Returns the char representation of the Character object
static int digit(char ch, int base)	Converts ch to int.
boolean equals(Object o)	Tests for equality between the objects.
static char forDigit(int digit, int base)	Returns the char representation of the digit in the specified base.
int hashCode()	Returns the hash code.
static boolean isDigit(char c)	Returns true if the char value is between 0 and 9
static boolean isJavaLetter(char c)	Returns true if the ch is a alphabet character, $, or _
static boolean isLetter(char c)	Returns true of the char is a letter
static boolean isLetterOrDigit(char c)	Returns true of the char is a letter or a digit
static boolean isLowerCase(char c)	Returns true of character is lower case.
static boolean isSpace(char c)	Returns true of the character is a space, tab, newline, or return
static boolean isUpperCase(char c)	Returns true of character is upper case.
static char toLowerCase(char c)	Converts a char to lower case.
String toString()	Returns the String representation of the Character
static char toUpperCase(char c)	Returns the Uppercase value of the Character
Double
final static double MAX_VALUE	returns the max value
final static MIN_VALUE	Returns the min value
final static double NaN	A double that is not a number
final static double NEGATIVE_INFINITY	-1.0/0.0
final static double POSITIVE_INFINITY	1.0/0.0
Double(double value)	Returns a Double representation of the double value.
Double (String s) throws NumberFormatExcepion	Returns a Double representation of the string value.
static long double doubleToLongBits(double value)	Returns the bit representation
double doubleValue()	Returns the double representation of the Double.
boolean equals(Object o)	Tests for equality
float floatValue()	Returns the float representation of the Double
int hashCode()	Returns the hash code
int intValue()	Returns the int representation of the Double.
boolean isInfinite()	Returns true if equal POSITIVE or NEGATIVE infinity
static boolean isInfinite(double d)	Returns true of true.
boolean isNaN()	Returns true if Double is NaN
static double longBitsToDouble(long l)	Double representation of the bits
long longValue()	Returns the long representation of the Double.
String toString()	Returns the String representation of the Double
static String toString(double d)	Converts d to String
static Double valueOf(String s) throws NumberFormatException	Converts String to Double
Float
final static float MAX_VALUE	returns the max value
final static float MIN_VALUE	Returns the min value
final static float NaN	A double that is not a number
final static float NEGATIVE_INFINITY	-1.0/0.0
final static float POSITIVE_INFINITY	1.0/0.0
Float(double value)	Returns a Float representation of the double value.
Float(float value)	Returns a Float representation of the float value.
Float (String s) throws NumberFormatExcepion	Returns a Float representation of the string value.
double doubleValue()	Returns the double representation of the Float.
boolean equals(Object o)	Tests for equality
static int floatToIntBits(float value)	Returns the bit representation
float floatValue()	Returns the float representation of the Float
int hashCode()	Returns the hash code
static float intBitsToFloat(int value)	Returns the float representation of the int bits
int intValue()	Returns the int representation of the Float.
boolean isInfinite()	Returns true if equal POSITIVE or NEGATIVE infinity
static boolean isInfinite(float f)	Returns true of true.
boolean isNaN()	Returns true if Double is NaN
long longValue()	Returns the long representation of the Float.
String toString()	Returns the String representation of the Float
static String toString(float f)	Converts f to String
static Float valueOf(String s) throws NumberFormatException	Converts String to Float
Integer
final static int MAX_VALUE	returns the max value
final static int MIN_VALUE	Returns the min value
Integer(int value)	Returns an Integer representation of the int value.
Integer (String s) throws NumberFormatExcepion	Returns an Integer representation of the String value.
double doubleValue()	Returns the double representation of the Integer.
boolean equals(Object o)	Tests for equality
float floatValue()	Returns the float representation of the Integer
static Integer getInteger(String propName)	Returns System property with given key
static Integer getInteger(String propName, int val)	Returns System property with given key
int hashCode()	Returns the hash code
int intValue()	Returns the int representation of the Integer.
long longValue()	Returns the long representation of the Integer.
static int parseInt(String s) throws NumberFormatException	Returns the int representation of the String
String toString()	Returns the String representation of the Integer
static String toString(int i)	Converts i to String
static Integer valueOf(String s) throws NumberFormatException	Converts String to Integer
Long
final static long MAX_VALUE	returns the max value
final static long MIN_VALUE	Returns the min value
Long(long value)	Returns a Long representation of the long value.
Long (String s) throws NumberFormatExcepion	Returns a Long representation of the String value.
double doubleValue()	Returns the double representation of the Long.
boolean equals(Object o)	Tests for equality
float floatValue()	Returns the float representation of the Long
static Long getLong(String propName)	Returns System property with given key
static Long getLong(String propName, long val)	Returns System property with given key
int hashCode()	Returns the hash code
int intValue()	Returns the int representation of the Long.
long longValue()	Returns the long representation of the Long.
static long parseLong(String s) throws NumberFormatException	Returns the long representation of the String
String toString()	Returns the String representation of the Long
static String toString(long l)	Converts l to String
static Long valueOf(String s) throws NumberFormatException	Converts String to Long

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Selena Sol contributes to the JavaBoutique's Introduction to Java. Selena curently works for Barclays Capital in London, one of the leading global investment banks in Europe and has worked as a software developer for the National Center for Human Genome research, Microline Software, Neuron Data, and Electric Eye in Singapore. Selena is perhaps best-known for creating the Public Domain Web Script Archive (Extropia) and writing several books on Web Programming (Perl, CGI, Java).
Email: selena@extropia.com

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