org.apache.commons.collections4.trie

## Class KeyAnalyzer<K>

- java.lang.Object
- - org.apache.commons.collections4.trie.KeyAnalyzer<K>

- All Implemented Interfaces:
    Serializable, Comparator<K>
  Direct Known Subclasses:
    StringKeyAnalyzer

      public abstract class KeyAnalyzer<K>
      extends Object
      implements Comparator<K>, Serializable

  Defines the interface to analyze `Trie` keys on a bit level. `KeyAnalyzer`'s methods return the length of the key in bits, whether or not a bit is set, and bits per element in the key.

  Additionally, a method determines if a key is a prefix of another key and returns the bit index where one key is different from another key (if the key and found key are equal than the return value is `EQUAL_BIT_KEY`).

  Since:
    4.0
  Version:
    $Id: KeyAnalyzer.java 1491621 2013-06-10 22:05:38Z tn $
  See Also:
    Serialized Form

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static int` | `EQUAL_BIT_KEY` Returned by `bitIndex(Object, int, int, Object, int, int)` if key and found key are equal.
    `static int` | `NULL_BIT_KEY` Returned by `bitIndex(Object, int, int, Object, int, int)` if key's bits are all 0.
    `static int` | `OUT_OF_BOUNDS_BIT_KEY`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `KeyAnalyzer()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `abstract int` | `bitIndex(K key, int offsetInBits, int lengthInBits, K other, int otherOffsetInBits, int otherLengthInBits)` Returns the n-th different bit between key and other.
    `abstract int` | `bitsPerElement()` Returns the number of bits per element in the key.
    `int` | `compare(K o1, K o2)`
    `abstract boolean` | `isBitSet(K key, int bitIndex, int lengthInBits)` Returns whether or not a bit is set.
    `abstract boolean` | `isPrefix(K prefix, int offsetInBits, int lengthInBits, K key)` Determines whether or not the given prefix (from offset to length) is a prefix of the given key.
    `abstract int` | `lengthInBits(K key)` Returns the length of the Key in bits.

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

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

    - ### Methods inherited from interface java.util.Comparator

      `equals`

- - ### Field Detail

    - #### NULL_BIT_KEY

          public static final int NULL_BIT_KEY

      Returned by `bitIndex(Object, int, int, Object, int, int)` if key's bits are all 0.
      See Also:
        Constant Field Values

    - #### EQUAL_BIT_KEY

          public static final int EQUAL_BIT_KEY

      Returned by `bitIndex(Object, int, int, Object, int, int)` if key and found key are equal. This is a very very specific case and shouldn't happen on a regular basis.
      See Also:
        Constant Field Values

    - #### OUT_OF_BOUNDS_BIT_KEY

          public static final int OUT_OF_BOUNDS_BIT_KEY

      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### KeyAnalyzer

          public KeyAnalyzer()

  - ### Method Detail

    - #### bitsPerElement

          public abstract int bitsPerElement()

      Returns the number of bits per element in the key. This is only useful for variable-length keys, such as Strings.
      Returns:
        the number of bits per element

    - #### lengthInBits

          public abstract int lengthInBits(K key)

      Returns the length of the Key in bits.
      Parameters:
        `key` - the key
      Returns:
        the bit length of the key

    - #### isBitSet

          public abstract boolean isBitSet(K key,
                         int bitIndex,
                         int lengthInBits)

      Returns whether or not a bit is set.
      Parameters:
        `key` - the key to check, may not be null
        `bitIndex` - the bit index to check
        `lengthInBits` - the maximum key length in bits to check
      Returns:
        `true` if the bit is set in the given key and `bitIndex` < `lengthInBits`, `false` otherwise.

    - #### bitIndex

          public abstract int bitIndex(K key,
                     int offsetInBits,
                     int lengthInBits,
                     K other,
                     int otherOffsetInBits,
                     int otherLengthInBits)

      Returns the n-th different bit between key and other. This starts the comparison in key at 'offsetInBits' and goes for 'lengthInBits' bits, and compares to the other key starting at 'otherOffsetInBits' and going for 'otherLengthInBits' bits.
      Parameters:
        `key` - the key to use
        `offsetInBits` - the bit offset in the key
        `lengthInBits` - the maximum key length in bits to use
        `other` - the other key to use
        `otherOffsetInBits` - the bit offset in the other key
        `otherLengthInBits` - the maximum key length in bits for the other key
      Returns:
        the bit index where the key and other first differ

    - #### isPrefix

          public abstract boolean isPrefix(K prefix,
                         int offsetInBits,
                         int lengthInBits,
                         K key)

      Determines whether or not the given prefix (from offset to length) is a prefix of the given key.
      Parameters:
        `prefix` - the prefix to check
        `offsetInBits` - the bit offset in the key
        `lengthInBits` - the maximum key length in bits to use
        `key` - the key to check
      Returns:
        `true` if this is a valid prefix for the given key

    - #### compare

          public int compare(K o1,
                    K o2)

      Specified by:
        `compare` in interface `Comparator<K>`

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