org.apache.commons.configuration2.tree

## Class DefaultConfigurationKey

- java.lang.Object
- - org.apache.commons.configuration2.tree.DefaultConfigurationKey

-     public class DefaultConfigurationKey
      extends Object

  A simple class that supports creation of and iteration on configuration keys supported by a `DefaultExpressionEngine` object.

  For key creation the class works similar to a StringBuffer: There are several `appendXXXX()` methods with which single parts of a key can be constructed. All these methods return a reference to the actual object so they can be written in a chain. When using this methods the exact syntax for keys need not be known.

  This class also defines a specialized iterator for configuration keys. With such an iterator a key can be tokenized into its single parts. For each part it can be checked whether it has an associated index.

  Instances of this class are always associated with an instance of `DefaultExpressionEngine`, from which the current delimiters are obtained. So key creation and parsing is specific to this associated expression engine.

  Since:
    1.3

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `class` | `DefaultConfigurationKey.KeyIterator` A specialized iterator class for tokenizing a configuration key.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `DefaultConfigurationKey(DefaultExpressionEngine engine)` Creates a new instance of `DefaultConfigurationKey` and sets the associated expression engine.
    `DefaultConfigurationKey(DefaultExpressionEngine engine, String key)` Creates a new instance of `DefaultConfigurationKey` and sets the associated expression engine and an initial key.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `DefaultConfigurationKey` | `append(String property)` Appends the name of a property to this key.
    `DefaultConfigurationKey` | `append(String property, boolean escape)` Appends the name of a property to this key.
    `DefaultConfigurationKey` | `appendAttribute(String attr)` Appends an attribute to this configuration key.
    `DefaultConfigurationKey` | `appendIndex(int index)` Appends an index to this configuration key.
    `String` | `attributeName(String key)` Extracts the name of the attribute from the given attribute key.
    `DefaultConfigurationKey` | `commonKey(DefaultConfigurationKey other)` Returns a configuration key object that is initialized with the part of the key that is common to this key and the passed in key.
    `String` | `constructAttributeKey(String key)` Decorates the given key so that it represents an attribute.
    `DefaultConfigurationKey` | `differenceKey(DefaultConfigurationKey other)` Returns the "difference key" to a given key.
    `boolean` | `equals(Object obj)` Checks if two `ConfigurationKey` objects are equal.
    `DefaultExpressionEngine` | `getExpressionEngine()` Returns the associated default expression engine.
    `int` | `hashCode()` Returns the hash code for this object.
    `boolean` | `isAttributeKey(String key)` Tests if the specified key represents an attribute according to the current expression engine.
    `DefaultConfigurationKey.KeyIterator` | `iterator()` Returns an iterator for iterating over the single components of this configuration key.
    `int` | `length()` Returns the actual length of this configuration key.
    `void` | `setLength(int len)` Sets the new length of this configuration key.
    `String` | `toString()` Returns a string representation of this object.
    `String` | `trim(String key)` Removes delimiters at the beginning and the end of the specified key.
    `String` | `trimLeft(String key)` Removes leading property delimiters from the specified key.
    `String` | `trimRight(String key)` Removes trailing property delimiters from the specified key.

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

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### DefaultConfigurationKey

          public DefaultConfigurationKey(DefaultExpressionEngine engine)

      Creates a new instance of `DefaultConfigurationKey` and sets the associated expression engine.
      Parameters:
        `engine` - the expression engine (must not be null)
      Throws:
        `IllegalArgumentException` - if the expression engine is null

    - #### DefaultConfigurationKey

          public DefaultConfigurationKey(DefaultExpressionEngine engine,
                                         String key)

      Creates a new instance of `DefaultConfigurationKey` and sets the associated expression engine and an initial key.
      Parameters:
        `engine` - the expression engine (must not be null)
        `key` - the key to be wrapped
      Throws:
        `IllegalArgumentException` - if the expression engine is null

  - ### Method Detail

    - #### getExpressionEngine

          public DefaultExpressionEngine getExpressionEngine()

      Returns the associated default expression engine.
      Returns:
        the associated expression engine

    - #### append

          public DefaultConfigurationKey append(String property,
                                                boolean escape)

      Appends the name of a property to this key. If necessary, a property delimiter will be added. If the boolean argument is set to true, property delimiters contained in the property name will be escaped.
      Parameters:
        `property` - the name of the property to be added
        `escape` - a flag if property delimiters in the passed in property name should be escaped
      Returns:
        a reference to this object

    - #### append

          public DefaultConfigurationKey append(String property)

      Appends the name of a property to this key. If necessary, a property delimiter will be added. Property delimiters in the given string will not be escaped.
      Parameters:
        `property` - the name of the property to be added
      Returns:
        a reference to this object

    - #### appendIndex

          public DefaultConfigurationKey appendIndex(int index)

      Appends an index to this configuration key.
      Parameters:
        `index` - the index to be appended
      Returns:
        a reference to this object

    - #### appendAttribute

          public DefaultConfigurationKey appendAttribute(String attr)

      Appends an attribute to this configuration key.
      Parameters:
        `attr` - the name of the attribute to be appended
      Returns:
        a reference to this object

    - #### length

          public int length()

      Returns the actual length of this configuration key.
      Returns:
        the length of this key

    - #### setLength

          public void setLength(int len)

      Sets the new length of this configuration key. With this method it is possible to truncate the key, e.g. to return to a state prior calling some `append()` methods. The semantic is the same as the `setLength()` method of `StringBuilder`.
      Parameters:
        `len` - the new length of the key

    - #### commonKey

          public DefaultConfigurationKey commonKey(DefaultConfigurationKey other)

      Returns a configuration key object that is initialized with the part of the key that is common to this key and the passed in key.
      Parameters:
        `other` - the other key
      Returns:
        a key object with the common key part

    - #### differenceKey

          public DefaultConfigurationKey differenceKey(DefaultConfigurationKey other)

      Returns the "difference key" to a given key. This value is the part of the passed in key that differs from this key. There is the following relation: `other = key.commonKey(other) + key.differenceKey(other)` for an arbitrary configuration key `key`.
      Parameters:
        `other` - the key for which the difference is to be calculated
      Returns:
        the difference key

    - #### equals

          public boolean equals(Object obj)

      Checks if two `ConfigurationKey` objects are equal. Two instances of this class are considered equal if they have the same content (i.e. their internal string representation is equal). The expression engine property is not taken into account.
      Overrides:
        `equals` in class `Object`
      Parameters:
        `obj` - the object to compare
      Returns:
        a flag if both objects are equal

    - #### hashCode

          public int hashCode()

      Returns the hash code for this object.
      Overrides:
        `hashCode` in class `Object`
      Returns:
        the hash code

    - #### toString

          public String toString()

      Returns a string representation of this object. This is the configuration key as a plain string.
      Overrides:
        `toString` in class `Object`
      Returns:
        a string for this object

    - #### isAttributeKey

          public boolean isAttributeKey(String key)

      Tests if the specified key represents an attribute according to the current expression engine.
      Parameters:
        `key` - the key to be checked
      Returns:
        true if this is an attribute key, false otherwise

    - #### constructAttributeKey

          public String constructAttributeKey(String key)

      Decorates the given key so that it represents an attribute. Adds special start and end markers. The passed in string will be modified only if does not already represent an attribute.
      Parameters:
        `key` - the key to be decorated
      Returns:
        the decorated attribute key

    - #### attributeName

          public String attributeName(String key)

      Extracts the name of the attribute from the given attribute key. This method removes the attribute markers - if any - from the specified key.
      Parameters:
        `key` - the attribute key
      Returns:
        the name of the corresponding attribute

    - #### trimLeft

          public String trimLeft(String key)

      Removes leading property delimiters from the specified key.
      Parameters:
        `key` - the key
      Returns:
        the key with removed leading property delimiters

    - #### trimRight

          public String trimRight(String key)

      Removes trailing property delimiters from the specified key.
      Parameters:
        `key` - the key
      Returns:
        the key with removed trailing property delimiters

    - #### trim

          public String trim(String key)

      Removes delimiters at the beginning and the end of the specified key.
      Parameters:
        `key` - the key
      Returns:
        the key with removed property delimiters

    - #### iterator

          public DefaultConfigurationKey.KeyIterator iterator()

      Returns an iterator for iterating over the single components of this configuration key.
      Returns:
        an iterator for this key

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