001 /* java.beans.Expression
002 Copyright (C) 2004, 2005 Free Software Foundation, Inc.
003
004 This file is part of GNU Classpath.
005
006 GNU Classpath is free software; you can redistribute it and/or modify
007 it under the terms of the GNU General Public License as published by
008 the Free Software Foundation; either version 2, or (at your option)
009 any later version.
010
011 GNU Classpath is distributed in the hope that it will be useful, but
012 WITHOUT ANY WARRANTY; without even the implied warranty of
013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014 General Public License for more details.
015
016 You should have received a copy of the GNU General Public License
017 along with GNU Classpath; see the file COPYING. If not, write to the
018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019 02110-1301 USA.
020
021 Linking this library statically or dynamically with other modules is
022 making a combined work based on this library. Thus, the terms and
023 conditions of the GNU General Public License cover the whole
024 combination.
025
026 As a special exception, the copyright holders of this library give you
027 permission to link this library with independent modules to produce an
028 executable, regardless of the license terms of these independent
029 modules, and to copy and distribute the resulting executable under
030 terms of your choice, provided that you also meet, for each linked
031 independent module, the terms and conditions of the license of that
032 module. An independent module is a module which is not derived from
033 or based on this library. If you modify this library, you may extend
034 this exception to your version of the library, but you are not
035 obligated to do so. If you do not wish to do so, delete this
036 exception statement from your version. */
037
038 package java.beans;
039
040 /**
041 * <p>An Expression captures the execution of an object method
042 * that returns a value.</p>
043 *
044 * <p>It stores an object, the method to call, and the arguments to pass to
045 * the method.</p>
046 *
047 * <p>While this class can generally be used to describe method calls it is
048 * part of the XML serialization API.</p>
049 *
050 * @author Robert Schuster (robertschuster@fsfe.org)
051 * @since 1.4
052 */
053 public class Expression extends Statement
054 {
055 // This is a placeholder to indicate that value hasn't been set
056 // yet;
057 private static final Object UNSET = new Object();
058
059 // The value to return. This is equal to unset until getValue is called.
060 private Object value;
061
062 /**
063 * Constructor Constructs an Expression representing the invocation of
064 * object.methodName(arg[0], arg[1], ...); However, it will never be executed.
065 * Instead, value will always be returned.
066 *
067 * @param value
068 * The value to return.
069 * @param target
070 * The object to invoke the method on.
071 * @param methodName
072 * The object method to invoke.
073 * @param arguments
074 * An array of arguments to pass to the method.
075 */
076 public Expression(Object value, Object target, String methodName,
077 Object[] arguments)
078 {
079 super(target, methodName, arguments);
080 this.value = value;
081 }
082
083 /**
084 * Constructor Constructs an Expression representing the invocation of
085 * object.methodName(arg[0], arg[1], ...);
086 *
087 * @param target
088 * The object to invoke the method on.
089 * @param methodName
090 * The object method to invoke.
091 * @param arguments
092 * An array of arguments to pass to the method.
093 */
094 public Expression(Object target, String methodName, Object[] arguments)
095 {
096 super(target, methodName, arguments);
097 this.value = UNSET;
098 }
099
100 /**
101 * Return the result of executing the method. If the cached value has not yet
102 * been set, the method is executed in the same way as Statement.execute(),
103 * except that the value is cached, and then returned. If the value has been
104 * set, it is returned without executing the method again.
105 *
106 * @return the result of executing the method.
107 * @exception Exception
108 * if an error occurs
109 */
110 public Object getValue() throws Exception
111 {
112 if (value == UNSET)
113 value = doExecute();
114 return value;
115 }
116
117 /**
118 * Set the cached value to be returned by getValue()
119 *
120 * @param value
121 * the value to cache and return.
122 */
123 public void setValue(Object value)
124 {
125 this.value = value;
126 }
127
128 /**
129 * Return a string representation of this expression.
130 */
131 public String toString()
132 {
133 String result = super.toString();
134 if (value != UNSET)
135 return value.getClass().getName() + "=" + result;
136 return result;
137 }
138 }