| /* |
| * Copyright 2000-2007 Sun Microsystems, Inc. All Rights Reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Sun designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Sun in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| * CA 95054 USA or visit www.sun.com if you need additional information or |
| * have any questions. |
| */ |
| |
| package java.beans; |
| |
| /** |
| * An <code>Expression</code> object represents a primitive expression |
| * in which a single method is applied to a target and a set of |
| * arguments to return a result - as in <code>"a.getFoo()"</code>. |
| * <p> |
| * In addition to the properties of the super class, the |
| * <code>Expression</code> object provides a <em>value</em> which |
| * is the object returned when this expression is evaluated. |
| * The return value is typically not provided by the caller and |
| * is instead computed by dynamically finding the method and invoking |
| * it when the first call to <code>getValue</code> is made. |
| * |
| * @see #getValue |
| * @see #setValue |
| * |
| * @since 1.4 |
| * |
| * @author Philip Milne |
| */ |
| public class Expression extends Statement { |
| |
| private static Object unbound = new Object(); |
| |
| private Object value = unbound; |
| |
| /** |
| * Creates a new <code>Statement</code> object with a <code>target</code>, |
| * <code>methodName</code> and <code>arguments</code> as per the parameters. |
| * |
| * @param target The target of this expression. |
| * @param methodName The methodName of this expression. |
| * @param arguments The arguments of this expression. If <code>null</code> then an empty array will be used. |
| * |
| * @see #getValue |
| */ |
| @ConstructorProperties({"target", "methodName", "arguments"}) |
| public Expression(Object target, String methodName, Object[] arguments) { |
| super(target, methodName, arguments); |
| } |
| |
| /** |
| * Creates a new <code>Expression</code> object for a method |
| * that returns a result. The result will never be calculated |
| * however, since this constructor uses the <code>value</code> |
| * parameter to set the value property by calling the |
| * <code>setValue</code> method. |
| * |
| * @param value The value of this expression. |
| * @param target The target of this expression. |
| * @param methodName The methodName of this expression. |
| * @param arguments The arguments of this expression. If <code>null</code> then an empty array will be used. |
| * |
| * @see #setValue |
| */ |
| public Expression(Object value, Object target, String methodName, Object[] arguments) { |
| this(target, methodName, arguments); |
| setValue(value); |
| } |
| |
| /** |
| * If the value property of this instance is not already set, |
| * this method dynamically finds the method with the specified |
| * methodName on this target with these arguments and calls it. |
| * The result of the method invocation is first copied |
| * into the value property of this expression and then returned |
| * as the result of <code>getValue</code>. If the value property |
| * was already set, either by a call to <code>setValue</code> |
| * or a previous call to <code>getValue</code> then the value |
| * property is returned without either looking up or calling the method. |
| * <p> |
| * The value property of an <code>Expression</code> is set to |
| * a unique private (non-<code>null</code>) value by default and |
| * this value is used as an internal indication that the method |
| * has not yet been called. A return value of <code>null</code> |
| * replaces this default value in the same way that any other value |
| * would, ensuring that expressions are never evaluated more than once. |
| * <p> |
| * See the <code>excecute</code> method for details on how |
| * methods are chosen using the dynamic types of the target |
| * and arguments. |
| * |
| * @see Statement#execute |
| * @see #setValue |
| * |
| * @return The result of applying this method to these arguments. |
| */ |
| public Object getValue() throws Exception { |
| if (value == unbound) { |
| setValue(invoke()); |
| } |
| return value; |
| } |
| |
| /** |
| * Sets the value of this expression to <code>value</code>. |
| * This value will be returned by the getValue method |
| * without calling the method associated with this |
| * expression. |
| * |
| * @param value The value of this expression. |
| * |
| * @see #getValue |
| */ |
| public void setValue(Object value) { |
| this.value = value; |
| } |
| |
| /*pp*/ String instanceName(Object instance) { |
| return instance == unbound ? "<unbound>" : super.instanceName(instance); |
| } |
| |
| /** |
| * Prints the value of this expression using a Java-style syntax. |
| */ |
| public String toString() { |
| return instanceName(value) + "=" + super.toString(); |
| } |
| } |