Class NullFilterVisitor

  • All Implemented Interfaces:
    ExpressionVisitor, FilterVisitor
    Direct Known Subclasses:
    ExtractBoundsFilterVisitor, TimeRangeVisitor

    public abstract class NullFilterVisitor
    extends Object
    implements FilterVisitor, ExpressionVisitor
    Abstract implementation of FilterVisitor simple returns the provided data.

    This class can be used as is as a placeholder that does nothing:

     Integer one = (Integer) filter.accepts( NullFilterVisitor.NULL_VISITOR, 1 );
    The class can also be used as an alternative to DefaultFilterVisitor if you want to only walk part of the data structure:
     FilterVisitor allFids = new NullFilterVisitor(){
         public Object visit( Id filter, Object data ) {
             if( data == null) return null;
             Set set = (Set) data;
             return set;
     Set set = (Set) myFilter.accept(allFids, new HashSet());
     Set set2 = (Set) myFilter.accept(allFids, null ); // set2 will be null
    The base class provides implementations for:
    • walking And, Or, and Not data structures, returning null at any point will exit early
    • a default implementation for every other construct that will return the provided data
    Jody Garnett (Refractions Research)