com.google.gxp.compiler.util.ClassMap.java Source code

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Here is the source code for com.google.gxp.compiler.util.ClassMap.java

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/*
 * Copyright (C) 2008 Google Inc.
 *
 * 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.gxp.compiler.util;

import com.google.common.collect.Maps;

import java.io.Serializable;
import java.util.Map;

/**
 * Maps from classes to objects (not necessarily objects of that class).
 * Attempts to adhere to the Liskov Substitution principle in that requests for
 * a class that does not have any value associated with it will retrieve the
 * value for its nearest superclass.
 *
 * TODO(laurence): Make this implement Map? What should it mean to iterate over
 * one of these? The remove method also seems weird. Actualy, even put is a bit
 * funny. Should it wipe out settings for subclasses?
 *
 * @param <K> base class for keys
 * @param <V> type of values
 */
public class ClassMap<K, V> implements Serializable {
    private final Map<Class<?>, V> map;

    public ClassMap() {
        this.map = Maps.newIdentityHashMap();
    }

    public static <K, V> ClassMap<K, V> create() {
        return new ClassMap<K, V>();
    }

    public V put(Class<? extends K> key, V value) {
        if (key.isInterface()) {
            // Interfaces are disallowed because the semantics get really weird with
            // multiple inheritance.
            // TODO(laurence): Is there a way to statically enforce this?
            throw new IllegalArgumentException("ClassMap cannot use interfaces as keys!");
        }
        V result = map.put(key, value);
        if (result == null) {
            result = getImpl(key.getSuperclass());
        }
        return result;
    }

    public V get(Object key) {
        if (key instanceof Class) {
            return getImpl((Class<?>) key);
        } else {
            return null;
        }
    }

    private V getImpl(Class<?> key) {
        Class<?> superKey = key;
        while (superKey != null) {
            V result = map.get(superKey);
            if (result != null) {
                return result;
            }
            superKey = superKey.getSuperclass();
        }
        return null;
    }

    private static final long serialVersionUID = 1L;
}