001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 * 
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 * 
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.lang3.builder;
018
019/**
020 * <p>
021 * The Builder interface is designed to designate a class as a <em>builder</em> 
022 * object in the Builder design pattern. Builders are capable of creating and 
023 * configuring objects or results that normally take multiple steps to construct 
024 * or are very complex to derive. 
025 * </p>
026 * 
027 * <p>
028 * The builder interface defines a single method, {@link #build()}, that 
029 * classes must implement. The result of this method should be the final 
030 * configured object or result after all building operations are performed.
031 * </p>
032 * 
033 * <p>
034 * It is a recommended practice that the methods supplied to configure the 
035 * object or result being built return a reference to {@code this} so that
036 * method calls can be chained together.
037 * </p>
038 * 
039 * <p>
040 * Example Builder:
041 * <pre><code>
042 * class FontBuilder implements Builder&lt;Font&gt; {
043 *     private Font font;
044 *     
045 *     public FontBuilder(String fontName) {
046 *         this.font = new Font(fontName, Font.PLAIN, 12);
047 *     }
048 * 
049 *     public FontBuilder bold() {
050 *         this.font = this.font.deriveFont(Font.BOLD);
051 *         return this; // Reference returned so calls can be chained
052 *     }
053 *     
054 *     public FontBuilder size(float pointSize) {
055 *         this.font = this.font.deriveFont(pointSize);
056 *         return this; // Reference returned so calls can be chained
057 *     }
058 * 
059 *     // Other Font construction methods
060 * 
061 *     public Font build() {
062 *         return this.font;
063 *     }
064 * }
065 * </code></pre>
066 * 
067 * Example Builder Usage:
068 * <pre><code>
069 * Font bold14ptSansSerifFont = new FontBuilder(Font.SANS_SERIF).bold()
070 *                                                              .size(14.0f)
071 *                                                              .build();
072 * </code></pre>
073 *
074 * 
075 * @param <T> the type of object that the builder will construct or compute.
076 * 
077 * @since 3.0
078 * @version $Id$
079 */
080public interface Builder<T> {
081
082    /**
083     * Returns a reference to the object being constructed or result being 
084     * calculated by the builder.
085     * 
086     * @return the object constructed or result calculated by the builder.
087     */
088    T build();
089}