+++ /dev/null
-package org.apache.lucene.util;
-
-/**
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You 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.
- */
-
-import java.lang.reflect.Method;
-import java.util.Collections;
-import java.util.HashSet;
-import java.util.WeakHashMap;
-import java.util.Set;
-
-/**
- * A utility for keeping backwards compatibility on previously abstract methods
- * (or similar replacements).
- * <p>Before the replacement method can be made abstract, the old method must kept deprecated.
- * If somebody still overrides the deprecated method in a non-final class,
- * you must keep track, of this and maybe delegate to the old method in the subclass.
- * The cost of reflection is minimized by the following usage of this class:</p>
- * <p>Define <strong>static final</strong> fields in the base class ({@code BaseClass}),
- * where the old and new method are declared:</p>
- * <pre>
- * static final VirtualMethod<BaseClass> newMethod =
- * new VirtualMethod<BaseClass>(BaseClass.class, "newName", parameters...);
- * static final VirtualMethod<BaseClass> oldMethod =
- * new VirtualMethod<BaseClass>(BaseClass.class, "oldName", parameters...);
- * </pre>
- * <p>This enforces the singleton status of these objects, as the maintenance of the cache would be too costly else.
- * If you try to create a second instance of for the same method/{@code baseClass} combination, an exception is thrown.
- * <p>To detect if e.g. the old method was overridden by a more far subclass on the inheritance path to the current
- * instance's class, use a <strong>non-static</strong> field:</p>
- * <pre>
- * final boolean isDeprecatedMethodOverridden =
- * oldMethod.getImplementationDistance(this.getClass()) > newMethod.getImplementationDistance(this.getClass());
- *
- * <em>// alternatively (more readable):</em>
- * final boolean isDeprecatedMethodOverridden =
- * VirtualMethod.compareImplementationDistance(this.getClass(), oldMethod, newMethod) > 0
- * </pre>
- * <p>{@link #getImplementationDistance} returns the distance of the subclass that overrides this method.
- * The one with the larger distance should be used preferable.
- * This way also more complicated method rename scenarios can be handled
- * (think of 2.9 {@code TokenStream} deprecations).</p>
- *
- * @lucene.internal
- */
-public final class VirtualMethod<C> {
-
- private static final Set<Method> singletonSet = Collections.synchronizedSet(new HashSet<Method>());
-
- private final Class<C> baseClass;
- private final String method;
- private final Class<?>[] parameters;
- private final WeakHashMap<Class<? extends C>, Integer> cache =
- new WeakHashMap<Class<? extends C>, Integer>();
-
- /**
- * Creates a new instance for the given {@code baseClass} and method declaration.
- * @throws UnsupportedOperationException if you create a second instance of the same
- * {@code baseClass} and method declaration combination. This enforces the singleton status.
- * @throws IllegalArgumentException if {@code baseClass} does not declare the given method.
- */
- public VirtualMethod(Class<C> baseClass, String method, Class<?>... parameters) {
- this.baseClass = baseClass;
- this.method = method;
- this.parameters = parameters;
- try {
- if (!singletonSet.add(baseClass.getDeclaredMethod(method, parameters)))
- throw new UnsupportedOperationException(
- "VirtualMethod instances must be singletons and therefore " +
- "assigned to static final members in the same class, they use as baseClass ctor param."
- );
- } catch (NoSuchMethodException nsme) {
- throw new IllegalArgumentException(baseClass.getName() + " has no such method: "+nsme.getMessage());
- }
- }
-
- /**
- * Returns the distance from the {@code baseClass} in which this method is overridden/implemented
- * in the inheritance path between {@code baseClass} and the given subclass {@code subclazz}.
- * @return 0 iff not overridden, else the distance to the base class
- */
- public synchronized int getImplementationDistance(final Class<? extends C> subclazz) {
- Integer distance = cache.get(subclazz);
- if (distance == null) {
- cache.put(subclazz, distance = Integer.valueOf(reflectImplementationDistance(subclazz)));
- }
- return distance.intValue();
- }
-
- /**
- * Returns, if this method is overridden/implemented in the inheritance path between
- * {@code baseClass} and the given subclass {@code subclazz}.
- * <p>You can use this method to detect if a method that should normally be final was overridden
- * by the given instance's class.
- * @return {@code false} iff not overridden
- */
- public boolean isOverriddenAsOf(final Class<? extends C> subclazz) {
- return getImplementationDistance(subclazz) > 0;
- }
-
- private int reflectImplementationDistance(final Class<? extends C> subclazz) {
- if (!baseClass.isAssignableFrom(subclazz))
- throw new IllegalArgumentException(subclazz.getName() + " is not a subclass of " + baseClass.getName());
- boolean overridden = false;
- int distance = 0;
- for (Class<?> clazz = subclazz; clazz != baseClass && clazz != null; clazz = clazz.getSuperclass()) {
- // lookup method, if success mark as overridden
- if (!overridden) {
- try {
- clazz.getDeclaredMethod(method, parameters);
- overridden = true;
- } catch (NoSuchMethodException nsme) {
- }
- }
-
- // increment distance if overridden
- if (overridden) distance++;
- }
- return distance;
- }
-
- /**
- * Utility method that compares the implementation/override distance of two methods.
- * @return <ul>
- * <li>> 1, iff {@code m1} is overridden/implemented in a subclass of the class overriding/declaring {@code m2}
- * <li>< 1, iff {@code m2} is overridden in a subclass of the class overriding/declaring {@code m1}
- * <li>0, iff both methods are overridden in the same class (or are not overridden at all)
- * </ul>
- */
- public static <C> int compareImplementationDistance(final Class<? extends C> clazz,
- final VirtualMethod<C> m1, final VirtualMethod<C> m2)
- {
- return Integer.valueOf(m1.getImplementationDistance(clazz)).compareTo(m2.getImplementationDistance(clazz));
- }
-
-}
fnp / pylucene.git / blobdiff