PrefixTermEnum.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 IndexReader = Lucene.Net.Index.IndexReader;
using Term = Lucene.Net.Index.Term;

namespace Lucene.Net.Search
{
    
    /// <summary> Subclass of FilteredTermEnum for enumerating all terms that match the
    /// specified prefix filter term.
    /// <p/>
    /// Term enumerations are always ordered by Term.compareTo().  Each term in
    /// the enumeration is greater than all that precede it.
    /// 
    /// </summary>
    public class PrefixTermEnum:FilteredTermEnum
    {
        
        private Term prefix;
        private bool endEnum = false;
        
        public PrefixTermEnum(IndexReader reader, Term prefix)
        {
            this.prefix = prefix;
            
            SetEnum(reader.Terms(new Term(prefix.Field, prefix.Text)));
        }
        
        public override float Difference()
        {
            return 1.0f;
        }
        
        public override bool EndEnum()
        {
            return endEnum;
        }

        protected internal virtual Term PrefixTerm
        {
            get { return prefix; }
        }

        protected internal override bool TermCompare(Term term)
        {
            if ((System.Object) term.Field == (System.Object) prefix.Field && term.Text.StartsWith(prefix.Text))
            {
                return true;
            }
            endEnum = true;
            return false;
        }
    }
}