coherence::util::extractor::AbstractExtractor

AbstractExtractor Class Reference

#include <coherence/util/extractor/AbstractExtractor.hpp>

Inherits Object, ValueExtractor, QueryMapComparator, and PortableObject.

Inherited by AbstractCompositeExtractor, EntryExtractor, IdentityExtractor, KeyExtractor, and ReflectionExtractor.

List of all members.

Detailed Description

Abstract base for ValueExtractor implementations.

It provides common functionality that allows any extending extractor to be used as a value Comparator.

See also:: coherence.util.comparator.ChainedComparator
coherence.util.comparator.InverseComparator

Author:: djl 2008.03.10

Public Types

typedef spec::Handle Handle

AbstractExtractor Handle definition.

typedef spec::View View

AbstractExtractor View definition.

typedef spec::Holder Holder

AbstractExtractor Holder definition.

Public Member Functions

virtual Object::Holder extract (Object::Holder ohTarget) const =0

Extract the value from the passed object.

The returned value may be NULL.

Parameters:

ohTarget

an Object to retrieve the value from

Returns:: the extracted value; NULL is an acceptable value

Exceptions:

	ClassCastException	if this ValueExtractor is incompatible with the passed object to extract a value from and the implementation requires the passed object to be of a certain type
	Exception	if this ValueExtractor encounters an exception in the course of extracting the value
	IllegalArgumentException	if this ValueExtractor cannot handle the passed object for any other reason; an implementor should include a descriptive message

virtual int32_t compareEntries (QueryMap::Entry::View vEntry1, QueryMap::Entry::View vEntry2) const

Compare two entries based on the rules specified by Comparator.

If possible, use the coherence::util::QueryMap.Entry::extract() method to optimize the value extraction process.

This method is expected to be implemented by Comparator wrappers, such as ChainedComparator and InverseComparator, which simply pass on this invocation to the wrapped Comparator objects if they too implement this interface, or to invoke their default compare method passing the actual objects (not the extracted values) obtained from the extractor using the passed entries.

This interface is also expected to be implemented by ValueExtractor implementations that implement the Comparator interface. It is expected that in most cases, the Comparator wrappers will eventually terminate at (i.e. delegate to) ValueExtractors that also implement this interface.

Parameters:

	vEntry1	the first entry to compare values from; read-only
	vEntry2	the second entry to compare values from; read-only

Returns:: a negative integer, zero, or a positive integer as the first entry denotes a value that is is less than, equal to, or greater than the value denoted by the second entry

Exceptions:

	ClassCastException	if the arguments' types prevent them from being compared by this Comparator.
	IllegalArgumentException	if the extractor cannot handle the passed objects for any other reason; an implementor should include a descriptive message

virtual int32_t compare (Object::View v1, Object::View v2) const

Compare two Objects.

If both Objects are comparable with this Comparator, return < 0, 0 or > 0 if the first Object is less than, equal to, or greater than the second Object.

The general contract for this method is:

If either of two handles are NULL, a coherence::lang::NullPointerException shall be thrown;
If either of two Objects are not comparable with this Comparator, a coherence::lang::IllegalArgumentException shall be thrown;
It shall be consistent with the Object::equals() relation, i.e. compare(v1, v2) == 0 if and only if Object::equals(v1, v2) == true
The subsequent calls to this method shall return the same value until either of arguments changed
It shall be anti-symmetric, i.e. compare(v1, v2) == -compare(v2, v1)

A typical implementation of Comparator may look as follows:

 int32_t MyTypeComparator::compare(Object::View v1,
                                   Object::View v2) const
     {
     // compares instances of class MyType only
     if (!v1 || !v2)
         {
         COH_THROW(NullPointerException());
         }
     MyType::View vTypedObj1 = cast<MyType::View>(v1);
     MyType::View vTypedObj2 = cast<MyType::View>(v2);
     if (!vTypedObj1 || !vTypedObj1)
         {
         COH_THROW(IllegalArgumentException("Instances of MyType expected"));
         }
     // here we suppose that the state of the MyType is defined by
     // single field of integer type
     if (vTypedObj1->m_intField == vTypedObj2->m_intField)
         {
         return 0;
         }
     else if (vTypedObj1->m_intField < vTypedObj2->m_intField)
         {
         return -1;
         }
     else
         {
         return 1;
         }
     }

The documentation for this class was generated from the following file:

coherence/util/extractor/AbstractExtractor.hpp