## org.opengis.filter.expression
Class NilExpression

    Object
      NilExpression

All Implemented Interfaces:
  Serializable, Expression

    public final class NilExpression

extends Object
implements Expression, Serializable

Placeholder class used to represent a NIL expression, evaultates to `null`.

This placeholder class is allows data structures to avoid the use of `null`. Please note that Expression.NIL is not considered a Literal with value `null` (since the literal may have its value changed).

See Also:
  Serialized Form

Field Summary

Fields inherited from interface Expression
`NIL`

Method Summary
`Object` `accept(ExpressionVisitor visitor, Object extraData)` Accepts a visitor.
`boolean` `equals(Object other)` Equals is defined only against `Expression.NIL`.
`Object` `evaluate(Object object)` Returns `null`

`

`<T> T`

`

`evaluate(Object object, Class<T> context)`
Returns `null`

`int` `hashCode()` Returns `0` in order to agree with hashcode of `null`.
`String` `toString()`

Methods inherited from class Object
`clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

Method Detail

### accept

    public Object accept(ExpressionVisitor visitor,
                         Object extraData)

  Description copied from interface: `Expression`
  Accepts a visitor. Subclasses must implement with a method whose content is the following:

      return visitor.visit(this, extraData);

  Specified by:
    `accept` in interface `Expression`

### evaluate

    public Object evaluate(Object object)

  Returns `null`

  Specified by:
    `evaluate` in interface `Expression`

### evaluate

    public <T> T evaluate(Object object,
                          Class<T> context)

  Returns `null`

  Specified by:
    `evaluate` in interface `Expression`
  Type Parameters:
    `T` - The type of the returned object.
  Parameters:
    `object` - The object to evaluate the expression against.
    `context` - The type of the resulting value of the expression.
  Returns:
    Evaluates the given expression based on the content of the given object an an instance of `context`.

### equals

    public boolean equals(Object other)

  Equals is defined only against `Expression.NIL`.

  Overrides:
    `equals` in class `Object`
  Parameters:
    `other` -
  Returns:
    `true` for Expression.NIL

### hashCode

    public int hashCode()

  Returns `0` in order to agree with hashcode of `null`.

  Overrides:
    `hashCode` in class `Object`

### toString

    public String toString()

  Overrides:
    `toString` in class `Object`

Copyright © 1994-2008 Open Geospatial Consortium. All Rights Reserved.