AbstractSupplier.java

  1. /*
  2.  * Licensed to the Apache Software Foundation (ASF) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * The ASF licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *      http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */

  18. package org.apache.commons.io.build;

  20. import org.apache.commons.io.function.IOSupplier;

  22. /**
  23.  * Abstracts supplying an instance of {@code T}.
  24.  * <p>
  25.  * Extend this class to implement the builder pattern.
  26.  * </p>
  27.  * <p>
  28.  * For example, here is a builder, a domain class, and a test.
  29.  * </p>
  30.  * <p>
  31.  * The builder:
  32.  * </p>
  33.  * <pre>
  34.     &#47;**
  35.      &#42; Builds Foo instances.
  36.      &#42;&#47;
  37.     public static class Builder extends AbstractSupplier&#60;Foo, Builder&#62; {

  39.         private String bar1;
  40.         private String bar2;
  41.         private String bar3;

  43.         &#47;**
  44.          &#42; Builds a new Foo.
  45.          &#42;&#47;
  46.         &#64;Override
  47.         public Foo get() {
  48.             return new Foo(bar1, bar2, bar3);
  49.         }

  51.         public Builder setBar1(final String bar1) {
  52.             this.bar1 = bar1;
  53.             return this;
  54.         }

  56.         public Builder setBar2(final String bar2) {
  57.             this.bar2 = bar2;
  58.             return this;
  59.         }

  61.         public Builder setBar3(final String bar3) {
  62.             this.bar3 = bar3;
  63.             return this;
  64.         }
  65.     }
  66.  * </pre>
  67.  * <p>
  68.  * The domain class:
  69.  * </p>
  70.  * <pre>
  71.     &#47;**
  72.      &#42; Domain class.
  73.      &#42;&#47;
  74.     public class Foo {

  76.         public static Builder builder() {
  77.             return new Builder();
  78.         }

  80.         private final String bar1;
  81.         private final String bar2;
  82.         private final String bar3;

  84.         private Foo(final String bar1, final String bar2, final String bar3) {
  85.             this.bar1 = bar1;
  86.             this.bar2 = bar2;
  87.             this.bar3 = bar3;
  88.         }

  90.         public String getBar1() {
  91.             return bar1;
  92.         }

  94.         public String getBar2() {
  95.             return bar2;
  96.         }

  98.         public String getBar3() {
  99.             return bar3;
  100.         }

  102.     }
  103.  * </pre>
  104.  * <p>
  105.  * The test:
  106.  * </p>
  107.  * <pre>
  108.     &#64;Test
  109.     public void test() {
  110.         final Foo foo = Foo.builder()
  111.             .setBar1("value1")
  112.             .setBar2("value2")
  113.             .setBar3("value3")
  114.             .get();
  115.         assertEquals("value1", foo.getBar1());
  116.         assertEquals("value2", foo.getBar2());
  117.         assertEquals("value3", foo.getBar3());
  118.     }
  119.  * </pre>
  120.  *
  121.  * @param <T> the type of instances to build.
  122.  * @param <B> the type of builder subclass.
  123.  * @since 2.12.0
  124.  */
  125. public abstract class AbstractSupplier<T, B extends AbstractSupplier<T, B>> implements IOSupplier<T> {

  127.     /**
  128.      * Constructs a new instance for subclasses.
  129.      */
  130.     public AbstractSupplier() {
  131.         // empty
  132.     }

  134.     /**
  135.      * Returns this instance typed as the subclass type {@code B}.
  136.      * <p>
  137.      * This is the same as the expression:
  138.      * </p>
  139.      * <pre>
  140.      * (B) this
  141.      * </pre>
  142.      *
  143.      * @return this instance typed as the subclass type {@code B}.
  144.      */
  145.     @SuppressWarnings("unchecked")
  146.     protected B asThis() {
  147.         return (B) this;
  148.     }

  150. }
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