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 }