001 /*
002 * Copyright 2005 Stephen J. McConnell.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
013 * implied.
014 *
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019 package net.dpml.state;
020
021 import java.io.Serializable;
022
023
024 /**
025 * Default implemention of a state transition descriptor.
026 *
027 * @author <a href="http://www.dpml.net">Digital Product Meta Library</a>
028 * @version 1.2.0
029 */
030 public class DefaultTransition implements Transition, Serializable
031 {
032 private final String m_name;
033 private final String m_target;
034 private final Operation m_operation;
035
036 private transient State m_state;
037
038 /**
039 * Creation of a new transition.
040 * @param name the transition name
041 * @param target the transit target state name
042 */
043 public DefaultTransition( final String name, final String target )
044 {
045 this( name, target, null );
046 }
047
048 /**
049 * Creation of a new transition.
050 * @param name the transition name
051 * @param target the transit target state name
052 * @param operation optional transition operation
053 */
054 public DefaultTransition( final String name, final String target, final Operation operation )
055 {
056 if( null == name )
057 {
058 throw new NullPointerException( "name" );
059 }
060 if( null == target )
061 {
062 throw new NullPointerException( "target" );
063 }
064 m_name = name;
065 m_target = target;
066 m_operation = operation;
067 }
068
069 /**
070 * Set the state that this transition is a part of.
071 * @param state the owning state
072 */
073 public void setState( State state )
074 {
075 if( null == state )
076 {
077 throw new NullPointerException( "state" );
078 }
079 if( null == m_state )
080 {
081 m_state = state;
082 }
083 else
084 {
085 throw new IllegalStateException( "State already set." );
086 }
087 }
088
089 /**
090 * Return the state that this transition is a part of.
091 * @return the owning state
092 */
093 public State getState()
094 {
095 if( null != m_state )
096 {
097 return m_state;
098 }
099 else
100 {
101 throw new IllegalStateException( "Enclosing state has not been declared." );
102 }
103 }
104
105 /**
106 * Return the transition name
107 * @return the name
108 */
109 public String getName()
110 {
111 return m_name;
112 }
113
114 /**
115 * Return the transition target state name
116 * @return the target state name
117 */
118 public String getTargetName()
119 {
120 return m_target;
121 }
122
123 /**
124 * Return an operation associated with the transition.
125 * @return a possibly null operation
126 */
127 public Operation getOperation()
128 {
129 return m_operation;
130 }
131
132 /**
133 * Compare this object to another for equality.
134 * @param other the other object
135 * @return true if the object is equal to this object
136 */
137 public boolean equals( Object other )
138 {
139 if( null == other )
140 {
141 return false;
142 }
143 else if( other instanceof DefaultTransition )
144 {
145 DefaultTransition transition = (DefaultTransition) other;
146 if( !m_name.equals( transition.getName() ) )
147 {
148 return false;
149 }
150 else if( !equals( m_target, transition.getTargetName() ) )
151 {
152 return false;
153 }
154 else
155 {
156 return equals( m_operation, transition.getOperation() );
157 }
158 }
159 else
160 {
161 return false;
162 }
163 }
164
165 /**
166 * Compute the hashcode for this instance.
167 * @return the hashcode value
168 */
169 public int hashCode()
170 {
171 int hash = m_name.hashCode();
172 hash ^= m_target.hashCode();
173 if( m_operation != null )
174 {
175 hash ^= m_operation.hashCode();
176 }
177 return hash;
178 }
179
180 private boolean equals( Object a, Object b )
181 {
182 if( null == a )
183 {
184 return null == b;
185 }
186 else
187 {
188 return a.equals( b );
189 }
190 }
191
192 /**
193 * Return a string representation of the instance.
194 * @return the string value
195 */
196 public String toString()
197 {
198 return "transition:" + getName() + " (target=" + m_target + ")";
199 }
200 }