org.geotools.resources
Class ClassChanger<S extends java.lang.Comparable<S>,T extends java.lang.Number>

java.lang.Object
  extended by org.geotools.resources.ClassChanger<S,T>

public abstract class ClassChanger<S extends java.lang.Comparable<S>,T extends java.lang.Number>
extends java.lang.Object

A central place to register transformations between an arbitrary class and a Number. For example, it is sometime convenient to consider Date objects as if they were Long objects for computation purpose in generic algorithms. Client can call the following method to convert an arbitrary object to a Number:

 Object someArbitraryObject = new Date();
 Number myObjectAsANumber = ClassChanger.toNumber(someArbitraryObject);
 

Since:
2.0
Version:
$Id: ClassChanger.java 31015 2008-07-15 11:29:32Z desruisseaux $
Author:
Martin Desruisseaux (IRD)

Constructor Summary
protected ClassChanger(java.lang.Class<S> source, java.lang.Class<T> target)
          Constructs a new class changer.
 
Method Summary
static
<N extends java.lang.Number>
N
cast(java.lang.Number n, java.lang.Class<N> c)
          Casts the number to the specified class.
protected abstract  T convert(S object)
          Returns the numerical value for an object.
static java.lang.Class<? extends java.lang.Number> getFinestClass(java.lang.Class<? extends java.lang.Number> c1, java.lang.Class<? extends java.lang.Number> c2)
          Returns the class of the finest type.
static java.lang.Class<? extends java.lang.Number> getFinestClass(double value)
          Returns the smallest class capable to hold the specified value.
static java.lang.Class<?> getTransformedClass(java.lang.Class<?> source)
          Returns the target class for the specified source class, if a suitable transformation is known.
static java.lang.Class<? extends java.lang.Number> getWidestClass(java.lang.Class<? extends java.lang.Number> c1, java.lang.Class<? extends java.lang.Number> c2)
          Returns the class of the widest type.
static java.lang.Class<? extends java.lang.Number> getWidestClass(java.lang.Number n1, java.lang.Number n2)
          Returns the class of the widest type.
protected abstract  S inverseConvert(T value)
          Returns an instance of the converted classe from a numerical value.
static void register(ClassChanger<?,?> converter)
          Registers a new converter.
static
<C extends java.lang.Comparable>
C
toComparable(java.lang.Number value, java.lang.Class<C> classe)
          Wraps the specified number as an instance of the specified classe.
static java.lang.Number toNumber(java.lang.Comparable<?> object)
          Returns the numeric value for the specified object.
static java.lang.Class<?> toPrimitive(java.lang.Class<?> c)
          Converts a wrapper class to a primitive class.
 java.lang.String toString()
          Returns a string representation for this class changer.
static java.lang.Class<?> toWrapper(java.lang.Class<?> c)
          Converts a primitive class to a wrapper class.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

ClassChanger

protected ClassChanger(java.lang.Class<S> source,
                       java.lang.Class<T> target)
Constructs a new class changer.

Parameters:
source - Parent class for convert(S)'s input objects.
target - Parent class for convert(S)'s output objects.
Method Detail

convert

protected abstract T convert(S object)
                                               throws java.lang.ClassCastException
Returns the numerical value for an object.

Parameters:
object - Object to convert (may be null).
Returns:
The object's numerical value.
Throws:
java.lang.ClassCastException - if object is not of the expected class.

inverseConvert

protected abstract S inverseConvert(T value)
Returns an instance of the converted classe from a numerical value.

Parameters:
value - The value to wrap.
Returns:
An instance of the source classe.

toString

public java.lang.String toString()
Returns a string representation for this class changer.

Overrides:
toString in class java.lang.Object

register

public static void register(ClassChanger<?,?> converter)
                     throws java.lang.IllegalStateException
Registers a new converter. All registered ClassChanger will be taken in account by the toNumber(java.lang.Comparable) method. The example below register a conversion for the Date class:
  ClassChanger.register(new ClassChanger(Date.class, Long.class) {
      protected Long convert(final Comparable o) {
          return ((Date) o).getTime();
      }
  
      protected Comparable inverseConvert(final Number number) {
          return new Date(number.longValue());
      }
  });
 

Parameters:
converter - The ClassChanger to add.
Throws:
java.lang.IllegalStateException - if an other ClassChanger was already registered for the same source class. This is usually not a concern since the registration usually take place during the class initialization ("static" constructor).

getTransformedClass

public static java.lang.Class<?> getTransformedClass(java.lang.Class<?> source)
Returns the target class for the specified source class, if a suitable transformation is known. The source class is a Comparable subclass that will be specified as input to convert(S). The target class is a Number subclass that will be returned as output by convert(S). If no suitable mapping is found, then source is returned.


toNumber

public static java.lang.Number toNumber(java.lang.Comparable<?> object)
                                 throws java.lang.ClassNotFoundException
Returns the numeric value for the specified object. For example the code toNumber(new Date()) returns the Date.getTime() value of the specified date object as a Long.

Parameters:
object - Object to convert (may be null).
Returns:
null if object was null; otherwise object if the supplied object is already an instance of Number; otherwise a new number with the numerical value.
Throws:
java.lang.ClassNotFoundException - if object is not an instance of a registered class.

toComparable

public static <C extends java.lang.Comparable> C toComparable(java.lang.Number value,
                                                              java.lang.Class<C> classe)
                                                   throws java.lang.ClassNotFoundException
Wraps the specified number as an instance of the specified classe. For example toComparable(new Long(time), Date.class) is equivalent to new Date(time). There is of course no point to use this method if the destination class is know at compile time. This method is useful for creating instance of classes choosen dynamically at run time.

Parameters:
value - The numerical value (may be null).
classe - The desired classe for return value.
Throws:
java.lang.ClassNotFoundException - if classe is not a registered class.

toPrimitive

public static java.lang.Class<?> toPrimitive(java.lang.Class<?> c)
                                      throws java.lang.IllegalArgumentException
Converts a wrapper class to a primitive class. For example this method converts Double.class to Double.TYPE.

Parameters:
c - The wrapper class.
Returns:
The primitive class.
Throws:
java.lang.IllegalArgumentException - if the specified class is not a wrapper for a primitive.

toWrapper

public static java.lang.Class<?> toWrapper(java.lang.Class<?> c)
                                    throws java.lang.IllegalArgumentException
Converts a primitive class to a wrapper class. For example this method converts Double.TYPE to Double.class.

Parameters:
c - The primitive class.
Returns:
The wrapper class.
Throws:
java.lang.IllegalArgumentException - if the specified class is not a primitive.

cast

public static <N extends java.lang.Number> N cast(java.lang.Number n,
                                                  java.lang.Class<N> c)
                                       throws java.lang.IllegalArgumentException
Casts the number to the specified class. The class must by one of Byte, Short, Integer, Long, Float or Double.

Throws:
java.lang.IllegalArgumentException

getWidestClass

public static java.lang.Class<? extends java.lang.Number> getWidestClass(java.lang.Number n1,
                                                                         java.lang.Number n2)
                                                                  throws java.lang.IllegalArgumentException
Returns the class of the widest type. Numbers n1 and n2 must be instance of any of Byte, Short, Integer, Long, Float or Double types. At most one of the argument can be null.

Throws:
java.lang.IllegalArgumentException

getWidestClass

public static java.lang.Class<? extends java.lang.Number> getWidestClass(java.lang.Class<? extends java.lang.Number> c1,
                                                                         java.lang.Class<? extends java.lang.Number> c2)
                                                                  throws java.lang.IllegalArgumentException
Returns the class of the widest type. Classes c1 and c2 must be of any of Byte, Short, Integer, Long, Float or Double types. At most one of the argument can be null.

Throws:
java.lang.IllegalArgumentException

getFinestClass

public static java.lang.Class<? extends java.lang.Number> getFinestClass(java.lang.Class<? extends java.lang.Number> c1,
                                                                         java.lang.Class<? extends java.lang.Number> c2)
                                                                  throws java.lang.IllegalArgumentException
Returns the class of the finest type. Classes c1 and c2 must be of any of Byte, Short, Integer, Long, Float or Double types. At most one of the argument can be null.

Throws:
java.lang.IllegalArgumentException

getFinestClass

public static java.lang.Class<? extends java.lang.Number> getFinestClass(double value)
Returns the smallest class capable to hold the specified value.



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