Class ArrayTrie<V>

  • Type Parameters:
    V - the entry type
    All Implemented Interfaces:
    Trie<V>

    public class ArrayTrie<V>
    extends AbstractTrie<V>

    A Trie String lookup data structure using a fixed size array.

    This implementation is always case insensitive and is optimal for a small number of fixed strings with few special characters. The Trie is stored in an array of lookup tables, each indexed by the next character of the key. Frequently used characters are directly indexed in each lookup table, whilst infrequently used characters must use a big character table.

    This Trie is very space efficient if the key characters are from ' ', '+', '-', ':', ';', '.', 'A' to 'Z' or 'a' to 'z'. Other ISO-8859-1 characters can be used by the key, but less space efficiently.

    This Trie is not Threadsafe and contains no mutual exclusion or deliberate memory barriers. It is intended for an ArrayTrie to be built by a single thread and then used concurrently by multiple threads and not mutated during that access. If concurrent mutations of the Trie is required external locks need to be applied.

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private static int[] __lookup
      The index lookup table, this maps a character as a byte (ISO-8859-1 or UTF8) to an index within a Trie row
      private char[][] _bigIndex
      A big index for each row.
      private java.lang.String[] _key
      The key (if any) for a Trie row.
      private char[] _rowIndex
      The Trie rows in a single array which allows a lookup of row,character to the next row in the Trie.
      private char _rows
      The number of rows allocated
      private V[] _value
      The value (if any) for a Trie row.
      private static int ROW_SIZE
      The Size of a Trie row is how many characters can be looked up directly without going to a big index.
    • Constructor Summary

      Constructors 
      Constructor Description
      ArrayTrie()  
      ArrayTrie​(int capacity)  
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()  
      V get​(java.lang.String s, int offset, int len)
      Get an exact match from a String key
      V get​(java.nio.ByteBuffer b, int offset, int len)
      Get an exact match from a segment of a ByteBuufer as key
      V getBest​(byte[] b, int offset, int len)
      Get the best match from key in a byte array.
      private V getBest​(int t, byte[] b, int offset, int len)  
      private V getBest​(int t, java.lang.String s, int offset, int len)  
      private V getBest​(int t, java.nio.ByteBuffer b, int offset, int len)  
      V getBest​(java.lang.String s, int offset, int len)
      Get the best match from key in a String.
      V getBest​(java.nio.ByteBuffer b, int offset, int len)
      Get the best match from key in a byte buffer.
      boolean isFull()  
      java.util.Set<java.lang.String> keySet()  
      private void keySet​(java.util.Set<java.lang.String> set, int t)  
      boolean put​(java.lang.String s, V v)
      Put an entry into the Trie
      java.lang.String toString()  
      private void toString​(java.lang.Appendable out, int t)  
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
    • Field Detail

      • ROW_SIZE

        private static final int ROW_SIZE
        The Size of a Trie row is how many characters can be looked up directly without going to a big index. This is set at 32 to cover case insensitive alphabet and a few other common characters.
        See Also:
        Constant Field Values
      • __lookup

        private static final int[] __lookup
        The index lookup table, this maps a character as a byte (ISO-8859-1 or UTF8) to an index within a Trie row
      • _rowIndex

        private final char[] _rowIndex
        The Trie rows in a single array which allows a lookup of row,character to the next row in the Trie. This is actually a 2 dimensional array that has been flattened to achieve locality of reference. The first ROW_SIZE entries are for row 0, then next ROW_SIZE entries are for row 1 etc. So in general instead of using _rows[row][index], we use _rows[row*ROW_SIZE+index] to look up the next row for a given character. The array is of characters rather than integers to save space.
      • _key

        private final java.lang.String[] _key
        The key (if any) for a Trie row. A row may be a leaf, a node or both in the Trie tree.
      • _value

        private final V[] _value
        The value (if any) for a Trie row. A row may be a leaf, a node or both in the Trie tree.
      • _bigIndex

        private char[][] _bigIndex
        A big index for each row. If a character outside of the lookup map is needed, then a big index will be created for the row, with 256 entries, one for each possible byte.
      • _rows

        private char _rows
        The number of rows allocated
    • Constructor Detail

      • ArrayTrie

        public ArrayTrie()
      • ArrayTrie

        public ArrayTrie​(int capacity)
        Parameters:
        capacity - The capacity of the trie, which at the worst case is the total number of characters of all keys stored in the Trie. The capacity needed is dependent of the shared prefixes of the keys. For example, a capacity of 6 nodes is required to store keys "foo" and "bar", but a capacity of only 4 is required to store "bar" and "bat".
    • Method Detail

      • clear

        public void clear()
      • put

        public boolean put​(java.lang.String s,
                           V v)
        Description copied from interface: Trie
        Put an entry into the Trie
        Parameters:
        s - The key for the entry
        v - The value of the entry
        Returns:
        True if the Trie had capacity to add the field.
      • get

        public V get​(java.lang.String s,
                     int offset,
                     int len)
        Description copied from interface: Trie
        Get an exact match from a String key
        Parameters:
        s - The key
        offset - The offset within the string of the key
        len - the length of the key
        Returns:
        the value for the string / offset / length
      • get

        public V get​(java.nio.ByteBuffer b,
                     int offset,
                     int len)
        Description copied from interface: Trie
        Get an exact match from a segment of a ByteBuufer as key
        Parameters:
        b - The buffer
        offset - The offset within the buffer of the key
        len - the length of the key
        Returns:
        The value or null if not found
      • getBest

        public V getBest​(byte[] b,
                         int offset,
                         int len)
        Description copied from interface: Trie
        Get the best match from key in a byte array. The key is assumed to by ISO_8859_1 characters.
        Specified by:
        getBest in interface Trie<V>
        Overrides:
        getBest in class AbstractTrie<V>
        Parameters:
        b - The buffer
        offset - The offset within the array of the key
        len - the length of the key
        Returns:
        The value or null if not found
      • getBest

        public V getBest​(java.nio.ByteBuffer b,
                         int offset,
                         int len)
        Description copied from interface: Trie
        Get the best match from key in a byte buffer. The key is assumed to by ISO_8859_1 characters.
        Parameters:
        b - The buffer
        offset - The offset within the buffer of the key
        len - the length of the key
        Returns:
        The value or null if not found
      • getBest

        public V getBest​(java.lang.String s,
                         int offset,
                         int len)
        Description copied from interface: Trie
        Get the best match from key in a String.
        Parameters:
        s - The string
        offset - The offset within the string of the key
        len - the length of the key
        Returns:
        The value or null if not found
      • getBest

        private V getBest​(int t,
                          java.lang.String s,
                          int offset,
                          int len)
      • getBest

        private V getBest​(int t,
                          byte[] b,
                          int offset,
                          int len)
      • getBest

        private V getBest​(int t,
                          java.nio.ByteBuffer b,
                          int offset,
                          int len)
      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object
      • toString

        private void toString​(java.lang.Appendable out,
                              int t)
      • keySet

        public java.util.Set<java.lang.String> keySet()
      • keySet

        private void keySet​(java.util.Set<java.lang.String> set,
                            int t)
      • isFull

        public boolean isFull()