| /* |
| * Copyright (c) 2000, 2013, Oracle and/or its affiliates. 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. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package java.beans; |
| |
| /** |
| * An {@code Expression} 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()"}. |
| * <p> |
| * In addition to the properties of the super class, the |
| * {@code Expression} 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} 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 {@link Expression} object |
| * for the specified target object to invoke the method |
| * specified by the name and by the array of arguments. |
| * <p> |
| * The {@code target} and the {@code methodName} values should not be {@code null}. |
| * Otherwise an attempt to execute this {@code Expression} |
| * will result in a {@code NullPointerException}. |
| * If the {@code arguments} value is {@code null}, |
| * an empty array is used as the value of the {@code arguments} property. |
| * |
| * @param target the target object of this expression |
| * @param methodName the name of the method to invoke on the specified target |
| * @param arguments the array of arguments to invoke the specified method |
| * |
| * @see #getValue |
| */ |
| @ConstructorProperties({"target", "methodName", "arguments"}) |
| public Expression(Object target, String methodName, Object[] arguments) { |
| super(target, methodName, arguments); |
| } |
| |
| /** |
| * Creates a new {@link Expression} object with the specified value |
| * for the specified target object to invoke the method |
| * specified by the name and by the array of arguments. |
| * The {@code value} value is used as the value of the {@code value} property, |
| * so the {@link #getValue} method will return it |
| * without executing this {@code Expression}. |
| * <p> |
| * The {@code target} and the {@code methodName} values should not be {@code null}. |
| * Otherwise an attempt to execute this {@code Expression} |
| * will result in a {@code NullPointerException}. |
| * If the {@code arguments} value is {@code null}, |
| * an empty array is used as the value of the {@code arguments} property. |
| * |
| * @param value the value of this expression |
| * @param target the target object of this expression |
| * @param methodName the name of the method to invoke on the specified target |
| * @param arguments the array of arguments to invoke the specified method |
| * |
| * @see #setValue |
| */ |
| public Expression(Object value, Object target, String methodName, Object[] arguments) { |
| this(target, methodName, arguments); |
| setValue(value); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * <p> |
| * If the invoked method completes normally, |
| * the value it returns is copied in the {@code value} property. |
| * Note that the {@code value} property is set to {@code null}, |
| * if the return type of the underlying method is {@code void}. |
| * |
| * @throws NullPointerException if the value of the {@code target} or |
| * {@code methodName} property is {@code null} |
| * @throws NoSuchMethodException if a matching method is not found |
| * @throws SecurityException if a security manager exists and |
| * it denies the method invocation |
| * @throws Exception that is thrown by the invoked method |
| * |
| * @see java.lang.reflect.Method |
| * @since 1.7 |
| */ |
| @Override |
| public void execute() throws Exception { |
| setValue(invoke()); |
| } |
| |
| /** |
| * 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}. If the value property |
| * was already set, either by a call to {@code setValue} |
| * or a previous call to {@code getValue} then the value |
| * property is returned without either looking up or calling the method. |
| * <p> |
| * The value property of an {@code Expression} is set to |
| * a unique private (non-{@code null}) 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} |
| * 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 execute} 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. |
| * @throws Exception if the method with the specified methodName |
| * throws an exception |
| */ |
| public Object getValue() throws Exception { |
| if (value == unbound) { |
| setValue(invoke()); |
| } |
| return value; |
| } |
| |
| /** |
| * Sets the value of this expression to {@code value}. |
| * 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(); |
| } |
| } |