/*

  * 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.

  */

 package org.apache.commons.id;

 /**

  * <code>StringIdentifierGenerator</code> that always returns the same

  * string.  Use with {@link CompositeIdentifierGenerator} to embed constant

  * string identifiers, or to add prefixes or suffixes.

  * <p> 

  * Null constant values are not allowed. The default

  * (assumed by the argumentless constructor) is an empty string.</p>

  * 

  * @author Commons-Id team

  * @version $Id$

  */

 public class ConstantIdentifierGenerator extends 

     AbstractStringIdentifierGenerator {

     /** 

      * Constant string value always returned by this generator.

      */

     private final String identifier;

     /**

      * Factory method to create a new <code>ConstantIdentifierGenerator</code>

      * with the given constant value.  Does not allow null values.

      * 

      * @param identifier constant value returned by the newly created generator.

      *      Must not be null.

      * @return a new ConstantIdentifierGenerator

      * @throws IllegalArgumentException if identifier is null

      */

     public static StringIdentifierGenerator getInstance(String identifier) {

         return new ConstantIdentifierGenerator(identifier);

     }

     /**

      * Creates a new ConstantIdentifierGenerator using the 

      * default (empty string) constant value.

      * 

      */

     public ConstantIdentifierGenerator() {

         super();

         this.identifier = "";

     }

     /**

      * Creates a new ConstantIdentifierGenerator using the

      * given constant value.

      * <p> 

      * Null constant values are not allowed.</p>

      * 

      * @param identifier constant value returned by the generator.  Must not

      *   be null.

      * @throws IllegalArgumentExeption if identifier is null

      */

     public ConstantIdentifierGenerator(String identifier) {

         super();

         if (identifier == null) {

             throw new IllegalArgumentException

                 ("Constant identifier value must not be null");

         }

         this.identifier = identifier;

     }

     public String nextStringIdentifier() {

         return identifier;

     }

     /**

      * Returns the length of the constant string returned by this generator.

      * If the constant is null or an empty string, 0 is returned.

      *

      * @return the length of the constant string returned by this generator

      */

     public long maxLength() {

        if (identifier == null) {

            return 0;

        } else {

            return identifier.length();

        }

     }

     /**

      * Returns the length of the constant string returned by this generator.

      * If the constant is null or an empty string, 0 is returned.

      *

      * @return the length of the constant string returned by this generator

      */

     public long minLength() {

         return maxLength();

     }     

 }