001 package ezvcard.util;
002
003 import java.lang.reflect.Field;
004 import java.lang.reflect.Modifier;
005 import java.util.ArrayList;
006 import java.util.Collection;
007 import java.util.Collections;
008
009 /*
010 Copyright (c) 2013, Michael Angstadt
011 All rights reserved.
012
013 Redistribution and use in source and binary forms, with or without
014 modification, are permitted provided that the following conditions are met:
015
016 1. Redistributions of source code must retain the above copyright notice, this
017 list of conditions and the following disclaimer.
018 2. Redistributions in binary form must reproduce the above copyright notice,
019 this list of conditions and the following disclaimer in the documentation
020 and/or other materials provided with the distribution.
021
022 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
023 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
024 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
025 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
026 ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
027 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
028 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
029 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
030 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
031 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
032 */
033
034 /**
035 * Manages objects that are like enums in that they are constant, but unlike
036 * enums in that new instances can be created during runtime. This class ensures
037 * that all instances of a class are unique, so they can be safely compared
038 * using "==" (provided their constructors are private). It mimics the
039 * "case class" feature in Scala.
040 * @author Michael Angstadt
041 *
042 * @param <T> the class
043 * @param <V> the value that the class holds (e.g. String)
044 */
045 public abstract class CaseClasses<T, V> {
046 protected final Class<T> clazz;
047 protected volatile Collection<T> preDefined = null;
048 protected Collection<T> runtimeDefined = null;
049
050 /**
051 * Creates a new case class collection.
052 * @param clazz the case class
053 */
054 public CaseClasses(Class<T> clazz) {
055 this.clazz = clazz;
056 }
057
058 /**
059 * Creates a new instance of the case class.
060 * @param value the value to give the instance
061 * @return the new instance
062 */
063 protected abstract T create(V value);
064
065 /**
066 * Determines if a value is associated with a case object.
067 * @param object the object
068 * @param value the value
069 * @return true if it matches, false if not
070 */
071 protected abstract boolean matches(T object, V value);
072
073 /**
074 * Searches for a case object by value, only looking at the case class'
075 * static constants (does not include runtime-defined objects).
076 * @param value the value
077 * @return the object or null if one wasn't found
078 */
079 public T find(V value) {
080 checkInit();
081
082 for (T obj : preDefined) {
083 if (matches(obj, value)) {
084 return obj;
085 }
086 }
087 return null;
088 }
089
090 /**
091 * Searches for a case object by value, creating a new object if one cannot
092 * be found.
093 * @param value the value
094 * @return the object
095 */
096 public T get(V value) {
097 T found = find(value);
098 if (found != null) {
099 return found;
100 }
101
102 synchronized (runtimeDefined) {
103 for (T obj : runtimeDefined) {
104 if (matches(obj, value)) {
105 return obj;
106 }
107 }
108
109 T created = create(value);
110 runtimeDefined.add(created);
111 return created;
112 }
113 }
114
115 /**
116 * Gets all the static constants of the case class.
117 * @return all static constants
118 */
119 public Collection<T> all() {
120 checkInit();
121 return preDefined;
122 }
123
124 private void checkInit() {
125 if (preDefined == null) {
126 synchronized (this) {
127 //"double check idiom" (Bloch p.283)
128 if (preDefined == null) {
129 init();
130 }
131 }
132 }
133 }
134
135 private void init() {
136 Collection<T> preDefined = new ArrayList<T>();
137 for (Field field : clazz.getFields()) {
138 int modifiers = field.getModifiers();
139 //@formatter:off
140 if (Modifier.isStatic(modifiers) &&
141 Modifier.isPublic(modifiers) &&
142 field.getDeclaringClass() == clazz &&
143 field.getType() == clazz) {
144 //@formatter:on
145 try {
146 Object obj = field.get(null);
147 if (obj != null) {
148 T c = clazz.cast(obj);
149 preDefined.add(c);
150 }
151 } catch (Exception ex) {
152 //reflection error
153 //should never be thrown because we check for "public static" and the correct type
154 throw new RuntimeException(ex);
155 }
156 }
157 }
158
159 runtimeDefined = new ArrayList<T>(0);
160 this.preDefined = Collections.unmodifiableCollection(preDefined);
161 }
162 }