Java Collection Contain containsAll(final Collection<?> coll1, final Collection<?> coll2)

Description

Returns true iff all elements of coll2 are also contained in coll1 .

License

Apache License

Parameter

Parameter	Description
coll1	the first collection, must not be null
coll2	the second collection, must not be null

Return

true iff the intersection of the collections has the same cardinality as the set of unique elements from the second collection

Declaration

public static boolean containsAll(final Collection<?> coll1, final Collection<?> coll2)

Method Source Code

//package com.java2s;
/*/*  w w  w.j a  v a  2s  . c  o m*/
 * 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.util.Collection;

import java.util.HashSet;
import java.util.Iterator;

import java.util.Set;

public class Main {
    /**
     * Returns <code>true</code> iff all elements of {@code coll2} are also contained
     * in {@code coll1}. The cardinality of values in {@code coll2} is not taken into account,
     * which is the same behavior as {@link Collection#containsAll(Collection)}.
     * <p>
     * In other words, this method returns <code>true</code> iff the
     * {@link #intersection} of <i>coll1</i> and <i>coll2</i> has the same cardinality as
     * the set of unique values from {@code coll2}. In case {@code coll2} is empty, {@code true}
     * will be returned.
     * <p>
     * This method is intended as a replacement for {@link Collection#containsAll(Collection)}
     * with a guaranteed runtime complexity of {@code O(n + m)}. Depending on the type of
     * {@link Collection} provided, this method will be much faster than calling
     * {@link Collection#containsAll(Collection)} instead, though this will come at the
     * cost of an additional space complexity O(n).
     *
     * @param coll1  the first collection, must not be null
     * @param coll2  the second collection, must not be null
     * @return <code>true</code> iff the intersection of the collections has the same cardinality
     *   as the set of unique elements from the second collection
     * @since 4.0
     */
    public static boolean containsAll(final Collection<?> coll1, final Collection<?> coll2) {
        if (coll2.isEmpty()) {
            return true;
        } else {
            final Iterator<?> it = coll1.iterator();
            final Set<Object> elementsAlreadySeen = new HashSet<Object>();
            for (final Object nextElement : coll2) {
                if (elementsAlreadySeen.contains(nextElement)) {
                    continue;
                }

                boolean foundCurrentElement = false;
                while (it.hasNext()) {
                    final Object p = it.next();
                    elementsAlreadySeen.add(p);
                    if (nextElement == null ? p == null : nextElement.equals(p)) {
                        foundCurrentElement = true;
                        break;
                    }
                }

                if (foundCurrentElement) {
                    continue;
                } else {
                    return false;
                }
            }
            return true;
        }
    }

    /**
     * Null-safe check if the specified collection is empty.
     * <p>
     * Null returns true.
     *
     * @param coll  the collection to check, may be null
     * @return true if empty or null
     * @since 3.2
     */
    public static boolean isEmpty(final Collection<?> coll) {
        return coll == null || coll.isEmpty();
    }
}

Java Collection Contain containsAll(final Collection coll1, final Collection coll2)