com.google.common.collect.ForwardingSortedMap.java Source code

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Here is the source code for com.google.common.collect.ForwardingSortedMap.java

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/*
 * Copyright (C) 2007 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.collect;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

import java.util.Comparator;
import java.util.NoSuchElementException;
import java.util.SortedMap;

import javax.annotation.Nullable;

/**
 * A sorted map which forwards all its method calls to another sorted map.
 * Subclasses should override one or more methods to modify the behavior of
 * the backing sorted map as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p><i>Warning:</i> The methods of {@code ForwardingSortedMap} forward
 * <i>indiscriminately</i> to the methods of the delegate. For example,
 * overriding {@link #put} alone <i>will not</i> change the behavior of {@link
 * #putAll}, which can lead to unexpected behavior. In this case, you should
 * override {@code putAll} as well, either providing your own implementation, or
 * delegating to the provided {@code standardPutAll} method.
 *
 * <p>Each of the {@code standard} methods, where appropriate, use the
 * comparator of the map to test equality for both keys and values, unlike
 * {@code ForwardingMap}.
 *
 * <p>The {@code standard} methods and the collection views they return are not
 * guaranteed to be thread-safe, even when all of the methods that they depend
 * on are thread-safe.
 *
 * @author Mike Bostock
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
public abstract class ForwardingSortedMap<K, V> extends ForwardingMap<K, V> implements SortedMap<K, V> {
    // TODO(lowasser): identify places where thread safety is actually lost

    /** Constructor for use by subclasses. */
    protected ForwardingSortedMap() {
    }

    @Override
    protected abstract SortedMap<K, V> delegate();

    @Override
    public Comparator<? super K> comparator() {
        return delegate().comparator();
    }

    @Override
    public K firstKey() {
        return delegate().firstKey();
    }

    @Override
    public SortedMap<K, V> headMap(K toKey) {
        return delegate().headMap(toKey);
    }

    @Override
    public K lastKey() {
        return delegate().lastKey();
    }

    @Override
    public SortedMap<K, V> subMap(K fromKey, K toKey) {
        return delegate().subMap(fromKey, toKey);
    }

    @Override
    public SortedMap<K, V> tailMap(K fromKey) {
        return delegate().tailMap(fromKey);
    }

    /**
     * A sensible implementation of {@link SortedMap#keySet} in terms of the methods of
     * {@code ForwardingSortedMap}. In many cases, you may wish to override
     * {@link ForwardingSortedMap#keySet} to forward to this implementation or a subclass thereof.
     *
     * @since 15.0
     */
    @Beta
    protected class StandardKeySet extends Maps.SortedKeySet<K, V> {
        /** Constructor for use by subclasses. */
        public StandardKeySet() {
            super(ForwardingSortedMap.this);
        }
    }

    // unsafe, but worst case is a CCE is thrown, which callers will be expecting
    @SuppressWarnings("unchecked")
    private int unsafeCompare(Object k1, Object k2) {
        Comparator<? super K> comparator = comparator();
        if (comparator == null) {
            return ((Comparable<Object>) k1).compareTo(k2);
        } else {
            return ((Comparator<Object>) comparator).compare(k1, k2);
        }
    }

    /**
     * A sensible definition of {@link #containsKey} in terms of the {@code
     * firstKey()} method of {@link #tailMap}. If you override {@link #tailMap},
     * you may wish to override {@link #containsKey} to forward to this
     * implementation.
     *
     * @since 7.0
     */
    @Override
    @Beta
    protected boolean standardContainsKey(@Nullable Object key) {
        try {
            // any CCE will be caught
            @SuppressWarnings("unchecked")
            SortedMap<Object, V> self = (SortedMap<Object, V>) this;
            Object ceilingKey = self.tailMap(key).firstKey();
            return unsafeCompare(ceilingKey, key) == 0;
        } catch (ClassCastException e) {
            return false;
        } catch (NoSuchElementException e) {
            return false;
        } catch (NullPointerException e) {
            return false;
        }
    }

    /**
     * A sensible default implementation of {@link #subMap(Object, Object)} in
     * terms of {@link #headMap(Object)} and {@link #tailMap(Object)}. In some
     * situations, you may wish to override {@link #subMap(Object, Object)} to
     * forward to this implementation.
     *
     * @since 7.0
     */
    @Beta
    protected SortedMap<K, V> standardSubMap(K fromKey, K toKey) {
        checkArgument(unsafeCompare(fromKey, toKey) <= 0, "fromKey must be <= toKey");
        return tailMap(fromKey).headMap(toKey);
    }
}