Predicate (Java SE 12 & JDK 12 )
Keywords: javax.sql.rowset.Predicate interface

Module java.sql.rowset
Package 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

  The `Predicate` 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 the `FilteredRowSet`. 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 int[] lo;
             private int[] hi;
             private int[] idx;

             public Range(int[] lo, int[] hi, int[] idx) {
                this.lo = lo;
                this.hi = hi;
                this.idx = idx;
             }

            public boolean evaluate(RowSet rs) {

                // Check the present row determine if it lies
                // within the filtering criteria.

                for (int i = 0; i < idx.length; i++) {
                   int value;
                   try {
                       value = (Integer) rs.getObject(idx[i]);
                   } catch (SQLException ex) {
                       Logger.getLogger(Range.class.getName()).log(Level.SEVERE, null, ex);
                       return false;
                   }

                   if (value < lo[i] && value > hi[i]) {
                       // outside of filter constraints
                       return false;
                   }
               }
               // Within filter constraints
              return true;
            }
         }

  The example above implements a simple range predicate. Note, that implementations should but are not required to provide `String` and integer index based constructors to provide for JDBC RowSet Implementation applications that use both column identification conventions.

  Since:
    1.5

- - ### Method Summary

    Modifier and Type | Method | Description
    --- | --- | ---
    `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 `FilteredRowSet` object internal methods (not public) that control the `RowSet` object'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.
      Parameters:
        `rs` - The `RowSet` to be evaluated
      Returns:
        `true` if there are more rows in the filter; `false` otherwise

    - #### evaluate

          boolean evaluate​(Object value,
                           int column)
                    throws SQLException

      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.

      The `FilteredRowSet` object will use this method internally while inserting new rows to a `FilteredRowSet` instance.

      Parameters:
        `value` - An `Object` value which needs to be checked, whether it can be part of this `FilterRowSet` object.
        `column` - a `int` object that must match the SQL index of a column in this `RowSet` object. This must have been passed to `Predicate` as one of the columns for filtering while initializing a `Predicate`
      Returns:
        `true` if row value lies within the filter; `false` otherwise
      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 `FilteredRowSet` object to check whether the value lies between the filtering criteria set using the setFilter method.

      The `FilteredRowSet` object will use this method internally while inserting new rows to a `FilteredRowSet` instance.

      Parameters:
        `value` - An `Object` value which needs to be checked, whether it can be part of this `FilterRowSet`.
        `columnName` - a `String` object that must match the SQL name of a column in this `RowSet`, ignoring case. This must have been passed to `Predicate` as one of the columns for filtering while initializing a `Predicate`
      Returns:
        `true` if value lies within the filter; `false` otherwise
      Throws:
        `SQLException` - if the column is not part of filtering criteria