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## net.sf.saxon.expr
Class FilterIterator

    java.lang.Object
      net.sf.saxon.expr.FilterIterator

All Implemented Interfaces:
  SequenceIterator

Direct Known Subclasses:
  FilterIterator.Leading, FilterIterator.NonNumeric

public class FilterIterator
extends java.lang.Object
implements SequenceIterator

A FilterIterator filters an input sequence using a filter expression. Note that a FilterIterator is not used where the filter is a constant number (PositionFilter is used for this purpose instead), so this class does no optimizations for numeric predicates.

Nested Class Summary
`static class` | `FilterIterator.Leading` Subclass to support the extension function saxon:leading, which terminates the iteration at the first item whose predicate is false
`static class` | `FilterIterator.NonNumeric` Subclass to handle the common special case where it is statically known that the filter cannot return a numeric value

Field Summary
`protected SequenceIterator` | `base`
`protected Expression` | `filter`
`protected XPathContext` | `filterContext`

Fields inherited from interface net.sf.saxon.om.SequenceIterator
`ATOMIZABLE, GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD`

Constructor Summary
`FilterIterator(SequenceIterator base, Expression filter, XPathContext context)` Constructor

Method Summary
`Item` | `current()` Get the current value in the sequence (the one returned by the most recent call on next()).
`SequenceIterator` | `getAnother()` Get another iterator to return the same nodes
`protected Item` | `getNextMatchingItem()` Get the next node that matches the filter predicate if there is one, or null if not.
`int` | `getProperties()` Get properties of this iterator, as a bit-significant integer.
`protected boolean` | `matches()` Determine whether the context item matches the filter predicate
`Item` | `next()` Get the next item if there is one
`int` | `position()` Get the current position.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### base

    protected SequenceIterator base

### filter

    protected Expression filter

### filterContext

    protected XPathContext filterContext

Constructor Detail

### FilterIterator

    public FilterIterator(SequenceIterator base,
                          Expression filter,
                          XPathContext context)

  Constructor

Parameters:
  `base` - An iteration of the items to be filtered
  `filter` - The expression defining the filter predicate
  `context` - The context in which the expression is being evaluated

Method Detail

### next

    public Item next()
              throws XPathException

  Get the next item if there is one

  Specified by:
    `next` in interface `SequenceIterator`
  Returns:
    the next item, or null if there are no more items. Once a call on next() has returned null, no further calls should be made. The preferred action for an iterator if subsequent calls on next() are made is to return null again, and all implementations within Saxon follow this rule.
  Throws:
    `XPathException` - if an error occurs retrieving the next item

### getNextMatchingItem

    protected Item getNextMatchingItem()
                                throws XPathException

  Get the next node that matches the filter predicate if there is one, or null if not.

  Throws:
    `XPathException`

### matches

    protected boolean matches()
                       throws XPathException

  Determine whether the context item matches the filter predicate

  Throws:
    `XPathException`

### current

    public Item current()

  Description copied from interface: `SequenceIterator`
  Get the current value in the sequence (the one returned by the most recent call on next()). This will be null before the first call of next(). This method does not change the state of the iterator.

  Specified by:
    `current` in interface `SequenceIterator`
  Returns:
    the current item, the one most recently returned by a call on next(). Returns null if next() has not been called, or if the end of the sequence has been reached.

### position

    public int position()

  Description copied from interface: `SequenceIterator`
  Get the current position. This will usually be zero before the first call on next(), otherwise it will be the number of times that next() has been called. Once next() has returned null, the preferred action is for subsequent calls on position() to return -1, but not all existing implementations follow this practice. (In particular, the EmptyIterator is stateless, and always returns 0 as the value of position(), whether or not next() has been called.)

  This method does not change the state of the iterator.

  Specified by:
    `position` in interface `SequenceIterator`
  Returns:
    the current position, the position of the item returned by the most recent call of next(). This is 1 after next() has been successfully called once, 2 after it has been called twice, and so on. If next() has never been called, the method returns zero. If the end of the sequence has been reached, the value returned will always be <= 0; the preferred value is -1.

### getAnother

    public SequenceIterator getAnother()
                                throws XPathException

  Get another iterator to return the same nodes

  Specified by:
    `getAnother` in interface `SequenceIterator`
  Returns:
    a SequenceIterator that iterates over the same items, positioned before the first item
  Throws:
    `XPathException` - if any error occurs

### getProperties

    public int getProperties()

  Get properties of this iterator, as a bit-significant integer.

  Specified by:
    `getProperties` in interface `SequenceIterator`
  Returns:
    the properties of this iterator. This will be some combination of properties such as `GROUNDED`, `LAST_POSITION_FINDER`, and `LOOKAHEAD`. It is always acceptable to return the value zero, indicating that there are no known special properties. It is acceptable for the properties of the iterator to change depending on its state.

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