Multisets.java

/*
 * JBoss, Home of Professional Open Source
 * Copyright 2010, Red Hat Middleware LLC, and individual contributors
 * by the @authors tag. See the copyright.txt in the distribution for a
 * full listing of individual contributors.
 *
 * 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 org.jboss.solder.util.collections;

import static org.jboss.solder.util.collections.Preconditions.checkArgument;

public class Multisets {

    private Multisets() {
    }

    /**
     * Implementation of the {@code equals}, {@code hashCode}, and
     * {@code toString} methods of {@link Multiset.Entry}.
     */
    abstract static class AbstractEntry<E> implements Multiset.Entry<E> {
        /**
         * Indicates whether an object equals this entry, following the behavior
         * specified in {@link Multiset.Entry#equals}.
         */
        @Override
        public boolean equals(Object object) {
            if (object instanceof Multiset.Entry<?>) {
                Multiset.Entry<?> that = (Multiset.Entry<?>) object;
                return this.getCount() == that.getCount()
                        && Objects.equal(this.getElement(), that.getElement());
            }
            return false;
        }

        /**
         * Return this entry's hash code, following the behavior specified in
         * {@link Multiset.Entry#hashCode}.
         */
        @Override
        public int hashCode() {
            E e = getElement();
            return ((e == null) ? 0 : e.hashCode()) ^ getCount();
        }

        /**
         * Returns a string representation of this multiset entry. The string
         * representation consists of the associated element if the associated count
         * is one, and otherwise the associated element followed by the characters
         * " x " (space, x and space) followed by the count. Elements and counts are
         * converted to strings as by {@code String.valueOf}.
         */
        @Override
        public String toString() {
            String text = String.valueOf(getElement());
            int n = getCount();
            return (n == 1) ? text : (text + " x " + n);
        }
    }


    static <E> boolean setCountImpl(Multiset<E> self, E element, int oldCount, int newCount) {
        checkNonnegative(oldCount, "oldCount");
        checkNonnegative(newCount, "newCount");

        if (self.count(element) == oldCount) {
            self.setCount(element, newCount);
            return true;
        } else {
            return false;
        }
    }

    static <E> int setCountImpl(Multiset<E> self, E element, int count) {
        checkNonnegative(count, "count");

        int oldCount = self.count(element);

        int delta = count - oldCount;
        if (delta > 0) {
            self.add(element, delta);
        } else if (delta < 0) {
            self.remove(element, -delta);
        }

        return oldCount;
    }

    static void checkNonnegative(int count, String name) {
        checkArgument(count >= 0, "%s cannot be negative: %s", name, count);
    }
}