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1   /*
2    * Grapht, an open source dependency injector.
3    * Copyright 2014-2015 various contributors (see CONTRIBUTORS.txt)
4    * Copyright 2010-2014 Regents of the University of Minnesota
5    *
6    * This program is free software; you can redistribute it and/or modify
7    * it under the terms of the GNU Lesser General Public License as
8    * published by the Free Software Foundation; either version 2.1 of the
9    * License, or (at your option) any later version.
10   *
11   * This program is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
13   * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
14   * details.
15   *
16   * You should have received a copy of the GNU General Public License along with
17   * this program; if not, write to the Free Software Foundation, Inc., 51
18   * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
19   */
20  package org.grouplens.grapht.reflect;
21  
22  import javax.inject.Provider;
23  
24  /**
25   * Abstract implementation of {@link SatisfactionVisitor}.  All methods delegate to
26   * {@link #visitDefault()}, which in turn returns a default value.
27   *
28   * @author <a href="http://grouplens.org">GroupLens Research</a>
29   * @since 0.5
30   */
31  public abstract class AbstractSatisfactionVisitor<T> implements SatisfactionVisitor<T> {
32      protected final T defaultValue;
33  
34      /**
35       * Construct a visitor with a null default.
36       */
37      public AbstractSatisfactionVisitor() {
38          this(null);
39      }
40  
41      /**
42       * Construct a visitor with the specified default value.
43       *
44       * @param dft The default value to be returned by {@link #visitDefault()}.
45       */
46      public AbstractSatisfactionVisitor(T dft) {
47          defaultValue = dft;
48      }
49  
50      /**
51       * Default method called when other methods are not overridden.  The default implementation
52       * returns the default value provided to {@link #AbstractSatisfactionVisitor(Object)}.
53       * @return The return value.
54       */
55      public T visitDefault() {
56          return defaultValue;
57      }
58  
59      @Override
60      public T visitNull() {
61          return visitDefault();
62      }
63  
64      @Override
65      public T visitClass(Class<?> clazz) {
66          return visitDefault();
67      }
68  
69      @Override
70      public T visitInstance(Object instance) {
71          return visitDefault();
72      }
73  
74      @Override
75      public T visitProviderClass(Class<? extends Provider<?>> pclass) {
76          return visitDefault();
77      }
78  
79      @Override
80      public T visitProviderInstance(Provider<?> provider) {
81          return visitDefault();
82      }
83  }