Oracle® Coherence Java API Reference
v3.5

E14977-01

com.tangosol.util.filter
Class LimitFilter

java.lang.Object
  extended by com.tangosol.util.Base
      extended by com.tangosol.util.BitHelper
          extended by com.tangosol.util.ExternalizableHelper
              extended by com.tangosol.util.filter.LimitFilter
All Implemented Interfaces:
ExternalizableLite, PortableObject, Filter, EntryFilter, IndexAwareFilter, java.io.Serializable, java.lang.Cloneable

public class LimitFilter
extends ExternalizableHelper
implements Filter, EntryFilter, IndexAwareFilter, ExternalizableLite, PortableObject, java.lang.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(java.util.Map mapIndexes, java.util.Set setKeys)
          Filter remaining keys using a Map of available indexes.
 int calculateEffectiveness(java.util.Map mapIndexes, java.util.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.
 java.lang.Object clone()
          Clone this filter.
 boolean evaluate(java.lang.Object o)
          Apply the test to the object.
 boolean evaluateEntry(java.util.Map.Entry entry)
          Apply the test to a Map Entry.
 java.lang.Object[] extractPage(java.util.Iterator iter)
          Extract a subset of the specified iterator to fit the filter's parameters (i.e.
 java.lang.Object[] extractPage(java.lang.Object[] aEntry)
          Extract a subset of the specified array to fit the filter's parameters (i.e.
 java.util.Set extractPage(java.util.Set set)
          Extract a subset of the specified set to fit the filter's parameters (i.e.
 java.lang.Object getBottomAnchor()
          Obtain the bottom anchor object, which is the last value object on the current page.
 java.util.Comparator getComparator()
          Obtain the Comparator used to partition the entry values into pages.
 java.lang.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).
 java.lang.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(java.io.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(java.lang.Object oAnchor)
          Set the bottom anchor object.
 void setComparator(java.util.Comparator comparator)
          Set the Comparator used to partition the values into pages.
 void setCookie(java.lang.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(java.lang.Object oAnchor)
          Set the top anchor object.
 java.lang.String toString()
          Return a human-readable description for this Filter.
 void writeExternal(java.io.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, rotateLeft, rotateLeft, rotateLeft, rotateRight, rotateRight, rotateRight, 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(java.lang.Object o)
Apply the test to the object.

Specified by:
evaluate in interface Filter
Parameters:
o - the object to test
Returns:
true if the test passes, false otherwise

evaluateEntry

public boolean evaluateEntry(java.util.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(java.util.Map mapIndexes,
                                  java.util.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:
an effectiveness estimate of how well this filter can use the specified indexes to filter the specified keys

applyIndex

public Filter applyIndex(java.util.Map mapIndexes,
                         java.util.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 java.util.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(java.util.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 java.lang.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(java.lang.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 java.lang.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(java.lang.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 java.lang.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(java.lang.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 java.lang.Object[] extractPage(java.lang.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 java.util.Set extractPage(java.util.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 java.lang.Object[] extractPage(java.util.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 java.lang.String toString()
Return a human-readable description for this Filter.

Returns:
a String description of the Filter

clone

public java.lang.Object clone()
Clone this filter.

Returns:
a clone of this filter

readExternal

public void readExternal(java.io.DataInput in)
                  throws java.io.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:
java.io.IOException - if an I/O exception occurs
java.io.NotActiveException - if the object is not in its initial state, and therefore cannot be deserialized into

writeExternal

public void writeExternal(java.io.DataOutput out)
                   throws java.io.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:
java.io.IOException - if an I/O exception occurs

readExternal

public void readExternal(PofReader in)
                  throws java.io.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:
java.io.IOException - if an I/O error occurs

writeExternal

public void writeExternal(PofWriter out)
                   throws java.io.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:
java.io.IOException - if an I/O error occurs

Oracle® Coherence Java API Reference
v3.5

E14977-01

Copyright © 2000, 2009, Oracle. All rights reserved.