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Predicate (Java Platform SE 6) - JDK 5 Documentation v6.0, Java 2 SDK 英文文档
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Java™ Platform Standard Ed. 6 |
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javax.sql.rowset
Interface Predicate
public interface Predicate
The standard interface that provides the framework for all
FilteredRowSet objects to describe their filters.
1.0 Background
ThePredicate interface is a standard interface that
applications can implement to define the filter they wish to apply to a
a FilteredRowSet object. A FilteredRowSet
object consumes implementations of this interface and enforces the
constraints defined in the implementation of the method evaluate.
A FilteredRowSet object enforces the filter constraints in a
bi-directional manner: It outputs only rows that are within
the constraints of the filter; and conversely, it inserts, modifies, or updates
only rows that are within the constraints of the filter.
2.0 Implementation Guidelines
In order to supply a predicate for theFilteredRowSet.
this interface must be implemented. At this time, the JDBC RowSet
Implementations (JSR-114) does not specify any standard filters definitions.
By specifying a standard means and mechanism for a range of filters to be
defined and deployed with both the reference and vendor implementations
of the FilteredRowSet interface, this allows for a flexible
and application motivated implementations of Predicate to emerge.
A sample implementation would look something like this:
public class Range implements Predicate {
private Object lo[];
private Object hi[];
private int idx[];
public Range(Object[] lo, Object[] hi, int[] idx) {
this.lo = lo;
this.hi = hi;
this.idx = idx;
}
public boolean evaluate(RowSet rs) {
CachedRowSet crs = (CachedRowSet)rs;
boolean bool1,bool2;
// Check the present row determine if it lies
// within the filtering criteria.
for (int i = 0; i < idx.length; i++) {
if ((rs.getObject(idx[i]) >= lo[i]) &&
(rs.getObject(idx[i]) >= hi[i]) {
bool1 = true; // within filter constraints
} else {
bool2 = true; // outside of filter constraints
}
}
if (bool2) {
return false;
} else {
return true;
}
}
The example above implements a simple range predicate. Note, that
implementations should but are not required to provider String
and integer index based constructors to provide for JDBC RowSet Implementation
applications that use both column identification conventions.
| Method Summary | |
|---|---|
boolean |
evaluate(Object value,
int column)
This method is called by a FilteredRowSet object
to check whether the value lies between the filtering criterion (or criteria
if multiple constraints exist) set using the setFilter() method. |
boolean |
evaluate(Object value,
String columnName)
This method is called by the FilteredRowSet object
to check whether the value lies between the filtering criteria set
using the setFilter method. |
boolean |
evaluate(RowSet rs)
This method is typically called a FilteredRowSet object
internal methods (not public) that control the RowSet object's
cursor moving from row to the next. |
| Method Detail |
|---|
evaluate
boolean evaluate(RowSet rs)
- This method is typically called a
FilteredRowSetobject internal methods (not public) that control theRowSetobject's cursor moving from row to the next. In addition, if this internal method moves the cursor onto a row that has been deleted, the internal method will continue to ove the cursor until a valid row is found.- Returns:
trueif there are more rows in the filter;falseotherwise
evaluate
boolean evaluate(Object value, int column) throws SQLException
- This method is called by a
FilteredRowSetobject to check whether the value lies between the filtering criterion (or criteria if multiple constraints exist) set using thesetFilter()method.The
FilteredRowSetobject will use this method internally while inserting new rows to aFilteredRowSetinstance.- Parameters:
value- AnObjectvalue which needs to be checked, whether it can be part of thisFilterRowSetobject.column- aintobject that must match the SQL index of a column in thisRowSetobject. This must have been passed toPredicateas one of the columns for filtering while initializing aPredicate- Returns:
trueifrow value lies within the filter;falseotherwise- Throws:
SQLException- if the column is not part of filtering criteria
evaluate
boolean evaluate(Object value, String columnName) throws SQLException
- This method is called by the
FilteredRowSetobject to check whether the value lies between the filtering criteria set using the setFilter method.The
FilteredRowSetobject will use this method internally while inserting new rows to aFilteredRowSetinstance.- Parameters:
value- AnObjectvalue which needs to be checked, whether it can be part of thisFilterRowSet.columnName- aStringobject that must match the SQL name of a column in thisRowSet, ignoring case. This must have been passed toPredicateas one of the columns for filtering while initializing aPredicate- Returns:
trueif value lies within the filter;falseotherwise- Throws:
SQLException- if the column is not part of filtering criteria
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Java™ Platform Standard Ed. 6 |
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Submit a bug or feature
For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright 2006 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.