1 /* 2 * Copyright (c) 1998, 2017, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 /** 27 * Contains classes related to developing <em>beans</em> -- components based on 28 * the JavaBeans architecture. A few of the classes are used by beans 29 * while they run in an application. For example, the event classes are used by 30 * beans that fire property and vetoable change events (see 31 * {@link java.beans.PropertyChangeEvent}). However, most of the classes in this 32 * package are meant to be used by a bean editor (that is, a development 33 * environment for customizing and putting together beans to create an 34 * application). In particular, these classes help the bean editor create a user 35 * interface that the user can use to customize the bean. For example, a bean 36 * may contain a property of a special type that a bean editor may not know how 37 * to handle. By using the {@code PropertyEditor} interface, a bean developer 38 * can provide an editor for this special type. 39 * <p> 40 * To minimize the resources used by a bean, the classes used by bean editors 41 * are loaded only when the bean is being edited. They are not needed while the 42 * bean is running in an application and therefore not loaded. This information 43 * is kept in what's called a bean-info (see {@link java.beans.BeanInfo}). 44 * <p> 45 * Unless explicitly stated, null values or empty Strings are not valid 46 * parameters for the methods in this package. You may expect to see exceptions 47 * if these parameters are used. 48 * 49 * <h2>Long-Term Persistence</h2> 50 * As of v1.4, the {@code java.beans} package provides support for <em>long-term 51 * persistence</em> -- reading and writing a bean as a textual representation of 52 * its property values. The property values are treated as beans, and are 53 * recursively read or written to capture their publicly available state. This 54 * approach is suitable for long-term storage because it relies only on public 55 * API, rather than the likely-to-change private implementation. 56 * 57 * <blockquote><hr><b>Note:</b> The persistence scheme cannot automatically 58 * instantiate custom inner classes, such as you might use for event handlers. 59 * By using the {@link java.beans.EventHandler} class instead of inner classes 60 * for custom event handlers, you can avoid this problem.<hr></blockquote> 61 * <p> 62 * You read and write beans in XML format using the 63 * {@link java.beans.XMLDecoder} and {@link java.beans.XMLEncoder} classes, 64 * respectively. One notable feature of the persistence scheme is that reading 65 * in a bean requires no special knowledge of the bean. 66 * <p> 67 * Writing out a bean, on the other hand, sometimes requires special knowledge 68 * of the bean's type. If the bean's state can be expressed using only the 69 * no-argument constructor and public getter and setter methods for properties, 70 * no special knowledge is required. Otherwise, the bean requires a custom 71 * <em>persistence delegate</em> -- an object that is in charge of writing out 72 * beans of a particular type. All classes provided in the JDK that descend from 73 * {@code java.awt.Component}, as well as all their properties, automatically 74 * have persistence delegates. 75 * <p> 76 * If you need (or choose) to provide a persistence delegate for a bean, you can 77 * do so either by using a {@link java.beans.DefaultPersistenceDelegate} 78 * instance or by creating your own subclass of {@code PersistenceDelegate}. If 79 * the only reason a bean needs a persistence delegate is because you want to 80 * invoke the bean's constructor with property values as arguments, you can 81 * create the bean's persistence delegate with the one-argument 82 * {@code DefaultPersistenceDelegate} constructor. Otherwise, you need to 83 * implement your own persistence delegate, for which you're likely to need the 84 * following classes: 85 * <dl> 86 * <dt>{@link java.beans.PersistenceDelegate}</dt> 87 * <dd>The abstract class from which all persistence delegates descend. Your 88 * subclass should use its knowledge of the bean's type to provide whatever 89 * {@code Statement}s and {@code Expression}s are necessary to create the 90 * bean and restore its state.</dd> 91 * <dt>{@link java.beans.Statement}</dt> 92 * <dd>Represents the invocation of a single method on an object. Includes 93 * a set of arguments to the method.</dd> 94 * <dt>{@link java.beans.Expression}</dt> 95 * <dd>A subclass of {@code Statement} used for methods that return a 96 * value.</dd> 97 * </dl> 98 * <p> 99 * Once you create a persistence delegate, you register it using the 100 * {@code setPersistenceDelegate} method of {@code XMLEncoder}. 101 * 102 * <h2>Related Documentation</h2> 103 * For overview, architecture, and tutorial documentation, please see: 104 * <ul> 105 * <li><a href="https://docs.oracle.com/javase/tutorial/javabeans/"> 106 * JavaBeans</a>, a trail in <em>The Java Tutorial</em>.</li> 107 * <li><a href="http://www.oracle.com/technetwork/java/persistence2-141443.html"> 108 * Long-Term Persistence</a>, an article in 109 * <em>The Swing Connection</em>.</li> 110 * </ul> 111 */ 112 package java.beans; 113