| /* java.lang.reflect.InvocationHandler - dynamically executes methods in | |
| proxy instances | |
| Copyright (C) 2001 Free Software Foundation, Inc. | |
| This file is part of GNU Classpath. | |
| GNU Classpath is free software; you can redistribute it and/or modify | |
| it under the terms of the GNU General Public License as published by | |
| the Free Software Foundation; either version 2, or (at your option) | |
| any later version. | |
| GNU Classpath 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 for more details. | |
| You should have received a copy of the GNU General Public License | |
| along with GNU Classpath; see the file COPYING. If not, write to the | |
| Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA | |
| 02110-1301 USA. | |
| Linking this library statically or dynamically with other modules is | |
| making a combined work based on this library. Thus, the terms and | |
| conditions of the GNU General Public License cover the whole | |
| combination. | |
| As a special exception, the copyright holders of this library give you | |
| permission to link this library with independent modules to produce an | |
| executable, regardless of the license terms of these independent | |
| modules, and to copy and distribute the resulting executable under | |
| terms of your choice, provided that you also meet, for each linked | |
| independent module, the terms and conditions of the license of that | |
| module. An independent module is a module which is not derived from | |
| or based on this library. If you modify this library, you may extend | |
| this exception to your version of the library, but you are not | |
| obligated to do so. If you do not wish to do so, delete this | |
| exception statement from your version. */ | |
| package java.lang.reflect; | |
| /** | |
| * This interface defines an invocation handler. Suppose you are using | |
| * reflection, and found a method that requires that its parameter | |
| * be an object of a given interface. You want to call this method, | |
| * but have no idea what classes implement that interface. So, you can | |
| * create a {@link Proxy} instance, a convenient way to dynamically | |
| * generate a class that meets all the necessary properties of that | |
| * interface. But in order for the proxy instance to do any good, it | |
| * needs to know what to do when interface methods are invoked! So, | |
| * this interface is basically a cool wrapper that provides runtime | |
| * code generation needed by proxy instances. | |
| * | |
| * <p>While this interface was designed for use by Proxy, it will also | |
| * work on any object in general.</p> | |
| * | |
| * <p>Hints for implementing this class:</p> | |
| * | |
| * <ul> | |
| * <li>Don't forget that Object.equals, Object.hashCode, and | |
| * Object.toString will call this handler. In particular, | |
| * a naive call to proxy.equals, proxy.hashCode, or proxy.toString | |
| * will put you in an infinite loop. And remember that string | |
| * concatenation also invokes toString.</li> | |
| * <li>Obey the contract of the Method object you are handling, or | |
| * the proxy instance will be forced to throw a | |
| * {@link NullPointerException}, {@link ClassCastException}, | |
| * or {@link UndeclaredThrowableException}.</li> | |
| * <li>Be prepared to wrap/unwrap primitives as necessary.</li> | |
| * <li>The Method object may be owned by a different interface than | |
| * what was actually used as the qualifying type of the method | |
| * invocation in the Java source code. This means that it might | |
| * not always be safe to throw an exception listed as belonging | |
| * to the method's throws clause.</li> | |
| * </ul> | |
| * | |
| * <p><small>For a fun time, create an InvocationHandler that handles the | |
| * methods of a proxy instance of the InvocationHandler interface!</small></p> | |
| * | |
| * @see Proxy | |
| * @see UndeclaredThrowableException | |
| * | |
| * @author Eric Blake (ebb9@email.byu.edu) | |
| * @since 1.3 | |
| * @status updated to 1.4 | |
| */ | |
| public interface InvocationHandler | |
| { | |
| /** | |
| * When a method is invoked on a proxy instance, it is wrapped and | |
| * this method is called instead, so that you may decide at runtime | |
| * how the original method should behave. | |
| * | |
| * @param proxy the instance that the wrapped method should be | |
| * invoked on. When this method is called by a Proxy object, | |
| * `proxy' will be an instance of {@link Proxy}, and oddly enough, | |
| * <code>Proxy.getInvocationHandler(proxy)</code> will return | |
| * <code>this</code>! | |
| * @param method the reflected method to invoke on the proxy. | |
| * When this method is called by a Proxy object, 'method' | |
| * will be the reflection object owned by the declaring | |
| * class or interface, which may be a supertype of the | |
| * interfaces the proxy directly implements. | |
| * @param args the arguments passed to the original method, or | |
| * <code>null</code> if the method takes no arguments. | |
| * (But also be prepared to handle a 0-length array). | |
| * Arguments of primitive type, such as <code>boolean</code> | |
| * or <code>int</code>, are wrapped in the appropriate | |
| * class such as {@link Boolean} or {@link Integer}. | |
| * @return whatever is necessary to return from the wrapped method. | |
| * If the wrapped method is <code>void</code>, the proxy | |
| * instance will ignore it. If the wrapped method returns | |
| * a primitive, this must be the correct wrapper type whose value | |
| * is exactly assignable to the appropriate type (no widening | |
| * will be performed); a null object in this case causes a | |
| * {@link NullPointerException}. In all remaining cases, if | |
| * the returned object is not assignment compatible to the | |
| * declared type of the original method, the proxy instance | |
| * will generate a {@link ClassCastException}. | |
| * @throws Throwable this interface is listed as throwing anything, | |
| * but the implementation should only throw unchecked | |
| * exceptions and exceptions listed in the throws clause of | |
| * all methods being overridden by the proxy instance. If | |
| * something is thrown that is not compatible with the throws | |
| * clause of all overridden methods, the proxy instance will | |
| * wrap the exception in an UndeclaredThrowableException. | |
| * Note that an exception listed in the throws clause of the | |
| * `method' parameter might not be declared in additional | |
| * interfaces also implemented by the proxy object. | |
| * | |
| * @see Proxy | |
| * @see UndeclaredThrowableException | |
| */ | |
| Object invoke(Object proxy, Method method, Object[] args) | |
| throws Throwable; | |
| } |