Package org.apache.sis.internal.converter

Class IdentityConverter<S extends T,T>

java.lang.Object
org.apache.sis.internal.converter.IdentityConverter<S,T>
Type Parameters:
S - the base type of source objects.
T - the base type of converted objects.
All Implemented Interfaces:
Serializable, Function<S,T>, ObjectConverter<S,T>
public final class IdentityConverter<S extends T,T> extends Object
An object converter which returns the source unchanged.

Immutability and thread safety

This class is immutable and thus inherently thread-safe.
Since:
0.3
Version:
0.3
Author:
Martin Desruisseaux (IRD, Geomatys)
See Also:

  • Constructor Details

    • IdentityConverter

      public IdentityConverter(Class<S> sourceClass, Class<T> targetClass, ObjectConverter<T,S> inverse)
      Creates a new identity converter.
      Parameters:
      sourceClass - the source class.
      targetClass - the target class.
      inverse - the inverse converter, or null if none.

  • Method Details

    • properties

      public Set<FunctionProperty> properties()
      Returns the properties of this converter. This method returns a new EnumSet instead of returning a constant, because creating EnumSet is cheap and the standard JDK implementation has optimizations for bulk operations between EnumSet instances. Those optimizations are lost (at least on JDK6) is we wrap the EnumSet in a Collections.unmodifiableSet view.
      Returns:
      the manners in which source values are mapped to target values.

    • inverse

      public ObjectConverter<T,S> inverse() throws UnsupportedOperationException
      Returns the inverse converter, if any.
      Specified by:
      inverse in interface ObjectConverter<S extends T,T>
      Returns:
      a converter for converting instances of T back to instances of S.
      Throws:
      UnsupportedOperationException - if this converter is not invertible.
      See Also:

    • apply

      public T apply(S source)
      Returns the given object unchanged.
      Parameters:
      source - the value to convert.
      Returns:
      the given value unchanged.

    • getSourceClass

      public final Class<S> getSourceClass()
      Returns the source class given at construction time.
      Specified by:
      getSourceClass in interface ObjectConverter<S,T>
      Returns:
      the type of objects to convert.

    • getTargetClass

      public final Class<T> getTargetClass()
      Returns the target class given at construction time.
      Specified by:
      getTargetClass in interface ObjectConverter<S,T>
      Returns:
      the type of converted objects.

    • equals

      public final boolean equals(Object other)
      Performs the comparisons documented in Object.equals(Object) with an additional check: if both objects to compare are SystemConverter, then also requires the two objects to be of the same class. We do that in order to differentiate the "ordinary" converters from the FallbackConverter.

      Implementation note

      This is admittedly a little bit convolved. A cleaner approach would have been to not allow the ConverterRegister hash map to contain anything else than ClassPair keys, but the current strategy of using the same instance for keys and values reduces a little bit the number of objects to create in the JVM. Another cleaner approach would have been to compare ObjectConverters in a separated method, but users invoking equals on our system converters could be surprised.

      Our equals(Object) definition have the following implications regarding the way to use the ConverterRegistry.converters map:

      • When searching for a converter of the same class than the key (as in the ConverterRegistry.findEquals(SystemConverter) method), then there is no restriction on the key that can be given to the Map.get(K) method. The Map is "normal".
      • When searching for a converter for a pair of source and target classes (as in ConverterRegistry.find(Class, Class)), the key shall be an instance of ClassPair instance (not a subclass).
      Parameters:
      other - the object to compare with this SystemConverter.
      Returns:
      true if the given object is a ClassPair or a converter of the same class than this, and both have the same source and target classes.

    • unique

      public ObjectConverter<S,T> unique()
      Returns an unique instance of this converter if one exists. If a converter already exists for the same source an target classes, then this converter is returned. Otherwise this converter is returned without being cached.
      Returns:
      the unique instance, or this if no unique instance can be found.
      See Also:
      • SystemConverter.unique()

    • readResolve

      protected final Object readResolve() throws ObjectStreamException
      Returns the singleton instance on deserialization, if any. If no instance already exist in the virtual machine, we do not cache the instance (for now) for security reasons.
      Returns:
      the object to use after deserialization.
      Throws:
      ObjectStreamException - if the serialized object defines an unknown data type.

    • hashCode

      public final int hashCode()
      Returns a hash code value for this ClassPair. See Object.equals(Object) javadoc for information on the scope of this method.
      Overrides:
      hashCode in class Object

    • toString

      public String toString()
      Returns a string representation for this entry. Used for formatting error messages.
      Overrides:
      toString in class Object