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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.
+ */
+package org.apache.commons.lang3.builder;
+
+/**
+ * The Builder interface is designed to designate a class as a <em>builder</em>
+ * object in the Builder design pattern. Builders are capable of creating and
+ * configuring objects or results that normally take multiple steps to construct
+ * or are very complex to derive.
+ *
+ * <p>
+ * The builder interface defines a single method, {@link #build()}, that
+ * classes must implement. The result of this method should be the final
+ * configured object or result after all building operations are performed.
+ * </p>
+ *
+ * <p>
+ * It is a recommended practice that the methods supplied to configure the
+ * object or result being built return a reference to {@code this} so that
+ * method calls can be chained together.
+ * </p>
+ *
+ * <p>
+ * Example Builder:
+ * <pre><code>
+ * class FontBuilder implements Builder&lt;Font&gt; {
+ *     private Font font;
+ *
+ *     public FontBuilder(String fontName) {
+ *         this.font = new Font(fontName, Font.PLAIN, 12);
+ *     }
+ *
+ *     public FontBuilder bold() {
+ *         this.font = this.font.deriveFont(Font.BOLD);
+ *         return this; // Reference returned so calls can be chained
+ *     }
+ *
+ *     public FontBuilder size(float pointSize) {
+ *         this.font = this.font.deriveFont(pointSize);
+ *         return this; // Reference returned so calls can be chained
+ *     }
+ *
+ *     // Other Font construction methods
+ *
+ *     public Font build() {
+ *         return this.font;
+ *     }
+ * }
+ * </code></pre>
+ *
+ * Example Builder Usage:
+ * <pre><code>
+ * Font bold14ptSansSerifFont = new FontBuilder(Font.SANS_SERIF).bold()
+ *                                                              .size(14.0f)
+ *                                                              .build();
+ * </code></pre>
+ *
+ * @param <T> the type of object that the builder will construct or compute.
+ *
+ * @since 3.0
+ */
+@FunctionalInterface
+public interface Builder<T> {
+
+    /**
+     * Returns a reference to the object being constructed or result being
+     * calculated by the builder.
+     *
+     * @return the object constructed or result calculated by the builder.
+     */
+    T build();
+}