Term.cs

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/* 
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;

using StringHelper = Lucene.Net.Util.StringHelper;

namespace Lucene.Net.Index
{
    
    /// <summary>A Term represents a word from text.  This is the unit of search.  It is
    /// composed of two elements, the text of the word, as a string, and the name of
    /// the field that the text occured in, an interned string.
    /// Note that terms may represent more than words from text fields, but also
    /// things like dates, email addresses, urls, etc.  
    /// </summary>
    [Serializable]
    public sealed class Term : System.IComparable<Term>
    {
        internal System.String field;
        internal System.String text;
        
        /// <summary>Constructs a Term with the given field and text.
        /// <p/>Note that a null field or null text value results in undefined
        /// behavior for most Lucene APIs that accept a Term parameter. 
        /// </summary>
        public Term(System.String fld, System.String txt)
        {
            field = StringHelper.Intern(fld);
            text = txt;
        }
        
        /// <summary>Constructs a Term with the given field and empty text.
        /// This serves two purposes: 1) reuse of a Term with the same field.
        /// 2) pattern for a query.
        /// 
        /// </summary>
        /// <param name="fld">
        /// </param>
        public Term(System.String fld):this(fld, "", true)
        {
        }
        
        internal Term(System.String fld, System.String txt, bool intern)
        {
            field = intern?StringHelper.Intern(fld):fld; // field names are interned
            text = txt; // unless already known to be
        }

        /// <summary>Returns the field of this term, an interned string.   The field indicates
        /// the part of a document which this term came from. 
        /// </summary>
        public string Field
        {
            get { return field; }
        }

        /// <summary>Returns the text of this term.  In the case of words, this is simply the
        /// text of the word.  In the case of dates and other types, this is an
        /// encoding of the object as a string.  
        /// </summary>
        public string Text
        {
            get { return text; }
        }

        /// <summary> Optimized construction of new Terms by reusing same field as this Term
        /// - avoids field.intern() overhead 
        /// </summary>
        /// <param name="text">The text of the new term (field is implicitly same as this Term instance)
        /// </param>
        /// <returns> A new Term
        /// </returns>
        public Term CreateTerm(System.String text)
        {
            return new Term(field, text, false);
        }
        
        //@Override
        public  override bool Equals(System.Object obj)
        {
            if (this == obj)
                return true;
            if (obj == null)
                return false;
            if (GetType() != obj.GetType())
                return false;
            Term other = (Term) obj;
            if (field == null)
            {
                if (other.field != null)
                    return false;
            }
            else if (!field.Equals(other.field))
                return false;
            if (text == null)
            {
                if (other.text != null)
                    return false;
            }
            else if (!text.Equals(other.text))
                return false;
            return true;
        }
        
        //@Override
        public override int GetHashCode()
        {
            int prime = 31;
            int result = 1;
            result = prime*result + ((field == null) ? 0 : field.GetHashCode());
            result = prime*result + ((text == null) ? 0 : text.GetHashCode());
            return result;
        }
        
        /// <summary>Compares two terms, returning a negative integer if this
        /// term belongs before the argument, zero if this term is equal to the
        /// argument, and a positive integer if this term belongs after the argument.
        /// The ordering of terms is first by field, then by text.
        /// </summary>
        public int CompareTo(Term other)
        {
            if ((System.Object) field == (System.Object) other.field)
            // fields are interned
                return String.CompareOrdinal(text, other.text);
            else
                return String.CompareOrdinal(field, other.field);
        }
        
        ///// <summary>Resets the field and text of a Term. </summary>
        //internal void  Set(System.String fld, System.String txt)
        //{
        //    field = fld;
        //    text = txt;
        //}
        
        public override System.String ToString()
        {
            return field + ":" + text;
        }
        
//      private void  ReadObject(System.IO.BinaryReader in_Renamed)
//      {
//          in_Renamed.defaultReadObject();
//          field = StringHelper.Intern(field);
//      }

        [System.Runtime.Serialization.OnDeserialized]
        internal void OnDeserialized(System.Runtime.Serialization.StreamingContext context)
        {
            field = StringHelper.Intern(field);
        }
    }
}