PositionIncrementAttribute.cs

Go to the documentation of this file.

/* 
 * 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 Attribute = Lucene.Net.Util.Attribute;
using TokenStream = Lucene.Net.Analysis.TokenStream;

namespace Lucene.Net.Analysis.Tokenattributes
{
    
    /// <summary>The positionIncrement determines the position of this token
    /// relative to the previous Token in a <see cref="TokenStream" />, used in phrase
    /// searching.
    /// 
    /// <p/>The default value is one.
    /// 
    /// <p/>Some common uses for this are:<list>
    /// 
    /// <item>Set it to zero to put multiple terms in the same position.  This is
    /// useful if, e.g., a word has multiple stems.  Searches for phrases
    /// including either stem will match.  In this case, all but the first stem's
    /// increment should be set to zero: the increment of the first instance
    /// should be one.  Repeating a token with an increment of zero can also be
    /// used to boost the scores of matches on that token.</item>
    /// 
    /// <item>Set it to values greater than one to inhibit exact phrase matches.
    /// If, for example, one does not want phrases to match across removed stop
    /// words, then one could build a stop word filter that removes stop words and
    /// also sets the increment to the number of stop words removed before each
    /// non-stop word.  Then exact phrase queries will only match when the terms
    /// occur with no intervening stop words.</item>
    /// 
    /// </list>
    /// </summary>
    [Serializable]
    public class PositionIncrementAttribute:Attribute, IPositionIncrementAttribute, System.ICloneable
    {
        private int positionIncrement = 1;

        /// <summary>Set the position increment. The default value is one.
        /// 
        /// </summary>
        /// <value> the distance from the prior term </value>
        public virtual int PositionIncrement
        {
            set
            {
                if (value < 0)
                    throw new System.ArgumentException("Increment must be zero or greater: " + value);
                this.positionIncrement = value;
            }
            get { return positionIncrement; }
        }

        public override void  Clear()
        {
            this.positionIncrement = 1;
        }
        
        public  override bool Equals(System.Object other)
        {
            if (other == this)
            {
                return true;
            }
            
            if (other is PositionIncrementAttribute)
            {
                return positionIncrement == ((PositionIncrementAttribute) other).positionIncrement;
            }
            
            return false;
        }
        
        public override int GetHashCode()
        {
            return positionIncrement;
        }
        
        public override void  CopyTo(Attribute target)
        {
            IPositionIncrementAttribute t = (IPositionIncrementAttribute) target;
            t.PositionIncrement = positionIncrement;
        }
        
        override public System.Object Clone()
        {
            PositionIncrementAttribute impl = new PositionIncrementAttribute();
            impl.positionIncrement = positionIncrement;
            return impl;
        }
    }
}