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/*
* Copyright (C) 2012 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.reflect;
import com.google.common.annotations.Beta;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import javax.annotation.Nullable;
/**
* Abstract implementation of {@link InvocationHandler} that handles {@link Object#equals},
* {@link Object#hashCode} and {@link Object#toString}.
*
* @author Ben Yu
* @since 12.0
*/
@Beta
public abstract class AbstractInvocationHandler implements InvocationHandler {
private static final Object[] NO_ARGS = {};
/**
* {@inheritDoc}
*
* <p><ul>
* <li>{@code proxy.hashCode()} delegates to {@link AbstractInvocationHandler#hashCode}
* <li>{@code proxy.toString()} delegates to {@link AbstractInvocationHandler#toString}
* <li>{@code proxy.equals(argument)} returns true if: <ul>
* <li>{@code proxy} and {@code argument} are of the same type
* <li>and {@link AbstractInvocationHandler#equals} returns true for the {@link
* InvocationHandler} of {@code argument}
* </ul>
* <li>other method calls are dispatched to {@link #handleInvocation}.
* </ul>
*/
@Override public final Object invoke(Object proxy, Method method, @Nullable Object[] args)
throws Throwable {
if (args == null) {
args = NO_ARGS;
}
if (args.length == 0 && method.getName().equals("hashCode")) {
return hashCode();
}
if (args.length == 1
&& method.getName().equals("equals")
&& method.getParameterTypes()[0] == Object.class) {
Object arg = args[0];
return proxy.getClass().isInstance(arg) && equals(Proxy.getInvocationHandler(arg));
}
if (args.length == 0 && method.getName().equals("toString")) {
return toString();
}
return handleInvocation(proxy, method, args);
}
/**
* {@link #invoke} delegates to this method upon any method invocation on the proxy instance,
* except {@link Object#equals}, {@link Object#hashCode} and {@link Object#toString}. The result
* will be returned as the proxied method's return value.
*
* <p>Unlike {@link #invoke}, {@code args} will never be null. When the method has no parameter,
* an empty array is passed in.
*/
protected abstract Object handleInvocation(Object proxy, Method method, Object[] args)
throws Throwable;
/**
* By default delegates to {@link Object#equals} so instances are only equal if they are
* identical. {@code proxy.equals(argument)} returns true if: <ul>
* <li>{@code proxy} and {@code argument} are of the same type
* <li>and this method returns true for the {@link InvocationHandler} of {@code argument}
* </ul>
* Subclasses can override this method to provide custom equality.
*/
@Override public boolean equals(Object obj) {
return super.equals(obj);
}
/**
* By default delegates to {@link Object#hashCode}. The dynamic proxies' {@code hashCode()} will
* delegate to this method. Subclasses can override this method to provide custom equality.
*/
@Override public int hashCode() {
return super.hashCode();
}
/**
* By default delegates to {@link Object#toString}. The dynamic proxies' {@code toString()} will
* delegate to this method. Subclasses can override this method to provide custom string
* representation for the proxies.
*/
@Override public String toString() {
return super.toString();
}
}
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