com.tangosol.util.filter
Class LimitFilter

java.lang.Object
  com.tangosol.util.Base
      com.tangosol.util.BitHelper
          com.tangosol.util.ExternalizableHelper
              com.tangosol.util.filter.LimitFilter

All Implemented Interfaces:

ExternalizableLite, PortableObject, Filter, EntryFilter, IndexAwareFilter, Serializable, Cloneable

public class LimitFilter
extends ExternalizableHelper
implements Filter, EntryFilter, IndexAwareFilter, ExternalizableLite, PortableObject, Cloneable

Filter which truncates the results of another filter. This filter is a mutable object that is modified by the query processor. Clients are supposed to hold a reference to this filter and repetitively pass it to query methods after setting a desired page context calling setPage(int), nextPage(), or previousPage().

Author:

gg 2002.12.06

Constructor Summary

LimitFilter()
Default constructor (necessary for the ExternalizableLite interface).

LimitFilter(Filter filter, int cPageSize)
Construct a limit filter.

Method Summary

Filter	applyIndex(Map mapIndexes, Set setKeys) Filter remaining keys using a Map of available indexes.
int	calculateEffectiveness(Map mapIndexes, Set setKeys) Given a Map of available indexes, determine if this IndexAwareFilter can use any of the indexes to assist in its processing, and if so, determine how effective the use of that index would be.
Object	clone() Clone this filter.
boolean	evaluate(Object o) Apply the test to the object.
boolean	evaluateEntry(Map.Entry entry) Apply the test to a Map Entry.
Object[]	extractPage(Iterator iter) Extract a subset of the specified iterator to fit the filter's parameters (i.e.
Object[]	extractPage(Object[] aEntry) Extract a subset of the specified array to fit the filter's parameters (i.e.
Set	extractPage(Set set) Extract a subset of the specified set to fit the filter's parameters (i.e.
Object	getBottomAnchor() Obtain the bottom anchor object, which is the last value object on the current page.
Comparator	getComparator() Obtain the Comparator used to partition the entry values into pages.
Object	getCookie() Obtain the cookie object.
Filter	getFilter() Obtain the Filter whose results are truncated by this filter.
int	getPage() Obtain a current page number (zero-based).
int	getPageSize() Obtain the page size (expressed as a number of entries per page).
Object	getTopAnchor() Obtain the top anchor object, which is the last value object on a previous page.
void	nextPage() Switch to the next page.
void	previousPage() Switch to the previous page.
void	readExternal(DataInput in) Restore the contents of this object by loading the object's state from the passed DataInput object.
void	readExternal(PofReader in) Restore the contents of a user type instance by reading its state using the specified PofReader object.
void	setBottomAnchor(Object oAnchor) Set the bottom anchor object.
void	setComparator(Comparator comparator) Set the Comparator used to partition the values into pages.
void	setCookie(Object oCookie) Set the cookie object.
void	setPage(int nPage) Set the page number (zero-based).
void	setPageSize(int cPageSize) Set the page size (expressed as a number of entries per page).
void	setTopAnchor(Object oAnchor) Set the top anchor object.
String	toString() Return a human-readable description for this Filter.
void	writeExternal(DataOutput out) Save the contents of this object by storing the object's state into the passed DataOutput object.
void	writeExternal(PofWriter out) Save the contents of a POF user type instance by writing its state using the specified PofWriter object.

Methods inherited from class com.tangosol.util.BitHelper

countBits, countBits, countBits, indexOfLSB, indexOfLSB, indexOfLSB, indexOfMSB, indexOfMSB, indexOfMSB, toBitString, toBitString, toBitString

Constructor Detail

LimitFilter

public LimitFilter()

Default constructor (necessary for the ExternalizableLite interface).

LimitFilter

public LimitFilter(Filter filter,
                   int cPageSize)

Construct a limit filter.

Parameters:

filter - the filter whose results this Filter truncates

Method Detail

evaluate

public boolean evaluate(Object o)

Apply the test to the object.

Specified by:

evaluate in interface Filter

Returns:

true if the test passes, false otherwise

evaluateEntry

public boolean evaluateEntry(Map.Entry entry)

Apply the test to a Map Entry.

Specified by:

evaluateEntry in interface EntryFilter

Parameters:

entry - the Map Entry to evaluate; never null

Returns:

true if the test passes, false otherwise

calculateEffectiveness

public int calculateEffectiveness(Map mapIndexes,
                                  Set setKeys)

Given a Map of available indexes, determine if this IndexAwareFilter can use any of the indexes to assist in its processing, and if so, determine how effective the use of that index would be.

The returned value is an effectiveness estimate of how well this filter can use the specified indexes to filter the specified keys. An operation that requires no more than a single access to the index content (i.e. Equals, NotEquals) has an effectiveness of one. Evaluation of a single entry is assumed to have an effectiveness that depends on the index implementation and is usually measured as a constant number of the single operations. This number is referred to as evaluation cost.

If the effectiveness of a filter evaluates to a number larger than the keySet.size() * <evaluation cost> then a user could avoid using the index and iterate through the keySet calling evaluate rather then applyIndex.

Specified by:

calculateEffectiveness in interface IndexAwareFilter

Parameters:

mapIndexes - the available MapIndex objects keyed by the related ValueExtractor; read-only

setKeys - the set of keys that will be filtered; read-only

Returns:

a effectiveness estimate of how well this filter can use the specified indexes to filter the specified keys

applyIndex

public Filter applyIndex(Map mapIndexes,
                         Set setKeys)

Filter remaining keys using a Map of available indexes.

The filter is responsible for removing all keys from the passed set of keys that the applicable indexes can prove should be filtered. If the filter does not fully evaluate the remaining keys using just the index information, it must return a filter (which may be an EntryFilter) that can complete the task using an iterating implementation. If, on the other hand, the filter does fully evaluate the remaining keys using just the index information, then it should return null to indicate that no further filtering is necessary.

Specified by:

applyIndex in interface IndexAwareFilter

Parameters:

mapIndexes - the available MapIndex objects keyed by the related ValueExtractor; read-only

setKeys - the mutable set of keys that remain to be filtered

Returns:

a Filter object (which may be an EntryFilter) that can be used to process the remaining keys, or null if no additional filter processing is necessary

getFilter

public Filter getFilter()

Obtain the Filter whose results are truncated by this filter.

Returns:

the filter whose results are truncated by this filter

getPageSize

public int getPageSize()

Obtain the page size (expressed as a number of entries per page).

Returns:

the page size

setPageSize

public void setPageSize(int cPageSize)

Set the page size (expressed as a number of entries per page).

Parameters:

cPageSize - the page size

getPage

public int getPage()

Obtain a current page number (zero-based).

Returns:

the page number

setPage

public void setPage(int nPage)

Set the page number (zero-based). Setting the page number to zero will reset the filter's state.

Parameters:

nPage - the page number

getComparator

public Comparator getComparator()

Obtain the Comparator used to partition the entry values into pages.

This method is intended to be used only by query processors. Clients should not modify the content of this property.

Returns:

the Comparator object

setComparator

public void setComparator(Comparator comparator)

Set the Comparator used to partition the values into pages.

This method is intended to be used only by query processors. Clients should not modify the content of this property.

Parameters:

comparator - Comparator object

getTopAnchor

public Object getTopAnchor()

Obtain the top anchor object, which is the last value object on a previous page.

This method is intended to be used only by query processors. Clients should not modify the content of this property.

Returns:

top anchor object

setTopAnchor

public void setTopAnchor(Object oAnchor)

Set the top anchor object.

This method is intended to be used only by query processors. Clients should not modify the content of this property.

Parameters:

oAnchor - the top anchor object

getBottomAnchor

public Object getBottomAnchor()

Obtain the bottom anchor object, which is the last value object on the current page.

This method is intended to be used only by query processors. Clients should not modify the content of this property.

Returns:

bottom anchor object

setBottomAnchor

public void setBottomAnchor(Object oAnchor)

Set the bottom anchor object.

This method is intended to be used only by query processors. Clients should not modify the content of this property.

Parameters:

oAnchor - the bottom anchor object

getCookie

public Object getCookie()

Obtain the cookie object.

This method is intended to be used only by query processors. Clients should not modify the content of this property.

Returns:

cookie object

setCookie

public void setCookie(Object oCookie)

Set the cookie object.

This method is intended to be used only by query processors. Clients should not modify the content of this property.

Parameters:

oCookie - the cookie object

nextPage

public void nextPage()

Switch to the next page.

previousPage

public void previousPage()

Switch to the previous page.

extractPage

public Object[] extractPage(Object[] aEntry)

Extract a subset of the specified array to fit the filter's parameters (i.e. page size and page number). If this filter has a comparator, the specified array is presumed to be sorted accordingly.

The returned array is guaranteed to iterate exactly in the same order as the original array.

Parameters:

aEntry - an original array of entries

Returns:

an array of entries extracted accordingly to the filter parameters

extractPage

public Set extractPage(Set set)

Extract a subset of the specified set to fit the filter's parameters (i.e. page size and page number). If this filter has a comparator, the specified Set is presumed to be sorted accordingly.

The returned set is guaranteed to iterate exactly in the same order as the original set.

Parameters:

set - an original set of entries

Returns:

a set of entries extracted accordingly to the filter parameters

extractPage

public Object[] extractPage(Iterator iter)

Extract a subset of the specified iterator to fit the filter's parameters (i.e. page size and page number). The returned array is guaranteed to iterate exactly in the same order as the original iterator.

Parameters:

iter - an original entry iterator

Returns:

an array of entries extracted accordingly to the filter parameters

toString

public String toString()

Return a human-readable description for this Filter.

Returns:

a String description of the Filter

clone

public Object clone()

Clone this filter.

Returns:

a clone of this filter

readExternal

public void readExternal(DataInput in)
                  throws IOException

Restore the contents of this object by loading the object's state from the passed DataInput object.

Specified by:

readExternal in interface ExternalizableLite

Parameters:

in - the DataInput stream to read data from in order to restore the state of this object

Throws:

IOException - if an I/O exception occurs

NotActiveException - if the object is not in its initial state, and therefore cannot be deserialized into

writeExternal

public void writeExternal(DataOutput out)
                   throws IOException

Save the contents of this object by storing the object's state into the passed DataOutput object.

Specified by:

writeExternal in interface ExternalizableLite

Parameters:

out - the DataOutput stream to write the state of this object to

Throws:

IOException - if an I/O exception occurs

readExternal

public void readExternal(PofReader in)
                  throws IOException

Restore the contents of a user type instance by reading its state using the specified PofReader object.

Specified by:

readExternal in interface PortableObject

Parameters:

in - the PofReader from which to read the object's state

Throws:

IOException - if an I/O error occurs

writeExternal

public void writeExternal(PofWriter out)
                   throws IOException

Save the contents of a POF user type instance by writing its state using the specified PofWriter object.

Specified by:

writeExternal in interface PortableObject

Parameters:

out - the PofWriter to which to write the object's state

Throws:

IOException - if an I/O error occurs