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author | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
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committer | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
commit | 554fd8c5195424bdbcabf5de30fdc183aba391bd (patch) | |
tree | 976dc5ab7fddf506dadce60ae936f43f58787092 /libjava/classpath/java/lang/reflect/InvocationHandler.java | |
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Diffstat (limited to 'libjava/classpath/java/lang/reflect/InvocationHandler.java')
-rw-r--r-- | libjava/classpath/java/lang/reflect/InvocationHandler.java | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/libjava/classpath/java/lang/reflect/InvocationHandler.java b/libjava/classpath/java/lang/reflect/InvocationHandler.java new file mode 100644 index 000000000..3d30afd93 --- /dev/null +++ b/libjava/classpath/java/lang/reflect/InvocationHandler.java @@ -0,0 +1,137 @@ +/* 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; + +} |