Package org.apache.commons.configuration2.interpol

# Enum DummyLookup

java.lang.Object
java.lang.Enum<DummyLookup>
org.apache.commons.configuration2.interpol.DummyLookup

All Implemented Interfaces:
  `Serializable`, `Comparable<DummyLookup>`, `Lookup`

public enum DummyLookup extends Enum<DummyLookup> implements Lookup

A simple dummy `Lookup` implementation.

This implementation always returns null for a passed in variable indicating that it cannot resolve that variable. This is useful for instance as an application of the null object pattern.

This class does not define any state, therefore a single instance can be shared. To enforce usage of only a single instance this class is actually an enumeration.

Since:
  2.0

- ## Enum Constant Summary

  Enum Constants
  Enum Constant
  Description
  `INSTANCE`
  The single instance of this class.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `Object`
  `lookup(String variable)`
  Looks up the value of the specified variable.
  `static DummyLookup`
  `valueOf(String name)`
  Returns the enum constant of this type with the specified name.
  `static DummyLookup[]`
  `values()`
  Returns an array containing the constants of this enum type, in the order they are declared.

  ### Methods inherited from class java.lang.Enum

  `clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf`

  ### Methods inherited from class java.lang.Object

  `getClass, notify, notifyAll, wait, wait, wait`

- ## Enum Constant Details

  - ### INSTANCE

    public static final DummyLookup INSTANCE
    The single instance of this class.

- ## Method Details

  - ### values

    public static DummyLookup[] values()
    Returns an array containing the constants of this enum type, in the order they are declared.
    Returns:
      an array containing the constants of this enum type, in the order they are declared

  - ### valueOf

    public static DummyLookup valueOf(String name)
    Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)
    Parameters:
      `name` - the name of the enum constant to be returned.
    Returns:
      the enum constant with the specified name
    Throws:
      `IllegalArgumentException` - if this enum type has no constant with the specified name
      `NullPointerException` - if the argument is null

  - ### lookup

    public Object lookup(String variable)
    Looks up the value of the specified variable. This method is called by `ConfigurationInterpolator` with the variable name extracted from the expression to interpolate (i.e. the prefix name has already been removed). A concrete implementation has to return the value of this variable or null if the variable name is unknown. This implementation always returns null.
    Specified by:
      `lookup` in interface `Lookup`
    Parameters:
      `variable` - the name of the variable to be resolved
    Returns:
      the value of this variable or null