1 /* java.beans.Expression 2 Copyright (C) 2004, 2005 Free Software Foundation, Inc. 3 4 This file is part of GNU Classpath. 5 6 GNU Classpath is free software; you can redistribute it and/or modify 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 2, or (at your option) 9 any later version. 10 11 GNU Classpath is distributed in the hope that it will be useful, but 12 WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 General Public License for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with GNU Classpath; see the file COPYING. If not, write to the 18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19 02110-1301 USA. 20 21 Linking this library statically or dynamically with other modules is 22 making a combined work based on this library. Thus, the terms and 23 conditions of the GNU General Public License cover the whole 24 combination. 25 26 As a special exception, the copyright holders of this library give you 27 permission to link this library with independent modules to produce an 28 executable, regardless of the license terms of these independent 29 modules, and to copy and distribute the resulting executable under 30 terms of your choice, provided that you also meet, for each linked 31 independent module, the terms and conditions of the license of that 32 module. An independent module is a module which is not derived from 33 or based on this library. If you modify this library, you may extend 34 this exception to your version of the library, but you are not 35 obligated to do so. If you do not wish to do so, delete this 36 exception statement from your version. */ 37 38 package java.beans; 39 40 /** 41 * <p>An Expression captures the execution of an object method 42 * that returns a value.</p> 43 * 44 * <p>It stores an object, the method to call, and the arguments to pass to 45 * the method.</p> 46 * 47 * <p>While this class can generally be used to describe method calls it is 48 * part of the XML serialization API.</p> 49 * 50 * @author Robert Schuster (robertschuster@fsfe.org) 51 * @since 1.4 52 */ 53 public class Expression extends Statement 54 { 55 // This is a placeholder to indicate that value hasn't been set 56 // yet; 57 private static final Object UNSET = new Object(); 58 59 // The value to return. This is equal to unset until getValue is called. 60 private Object value; 61 62 /** 63 * Constructor Constructs an Expression representing the invocation of 64 * object.methodName(arg[0], arg[1], ...); However, it will never be executed. 65 * Instead, value will always be returned. 66 * 67 * @param value 68 * The value to return. 69 * @param target 70 * The object to invoke the method on. 71 * @param methodName 72 * The object method to invoke. 73 * @param arguments 74 * An array of arguments to pass to the method. 75 */ Expression(Object value, Object target, String methodName, Object[] arguments)76 public Expression(Object value, Object target, String methodName, 77 Object[] arguments) 78 { 79 super(target, methodName, arguments); 80 this.value = value; 81 } 82 83 /** 84 * Constructor Constructs an Expression representing the invocation of 85 * object.methodName(arg[0], arg[1], ...); 86 * 87 * @param target 88 * The object to invoke the method on. 89 * @param methodName 90 * The object method to invoke. 91 * @param arguments 92 * An array of arguments to pass to the method. 93 */ Expression(Object target, String methodName, Object[] arguments)94 public Expression(Object target, String methodName, Object[] arguments) 95 { 96 super(target, methodName, arguments); 97 this.value = UNSET; 98 } 99 100 /** 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 */ getValue()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 */ setValue(Object value)123 public void setValue(Object value) 124 { 125 this.value = value; 126 } 127 128 /** 129 * Return a string representation of this expression. 130 */ toString()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 } 139