Collection comparison

Code

package org.darkmine.utils;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;

public class CollectionsComparisonUtils {

    /**
     * The result of a comparison.
     *
     * @param <T>
     */
    public static class Result<T> {
        private Collection<T> added;
        private Collection<T> removed;

        private Result(Collection<T> added, Collection<T> removed) {
            this.added = added;
            this.removed = removed;
        }

        /**
         * The items added to the collection.
         *
         * @return
         */
        public Collection<T> getAdded() {
            return added;
        }

        /**
         * The items removed from the collection.
         *
         * @return
         */
        public Collection<T> getRemoved() {
            return removed;
        }

        /**
         * The collections are the same.
         *
         * @return
         */
        public boolean isSame() {
            return added.size() + removed.size() == 0;
        }
    }

    /**
     * Implement this interface to determine if a collection contains an element or not.
     * @param <T>
     */
    public interface CollectionFinder<T> {
        boolean contains(Collection<T> collection,T element);
    }

    /**
     * The STANDARD_FINDER simply uses the Collections.contains() method.
     */
    private static final CollectionFinder STANDARD_FINDER = (collection, element) -> collection.contains( element );

    /**
     * Compare the contents of two collections (it does not matter about the order).
     *
     * @param older The older collection.
     * @param newer The newer collection.
     * @param <T>
     * @return
     */
    public static <T> Result<T> compareAnyOrder(Collection<T> older, Collection<T> newer) {
        return compareAnyOrder(older,newer,(CollectionFinder<T>) STANDARD_FINDER);
    }

    /**
     * Compare the contents of two collections (it does not matter about the order).
     *
     * @param older The older collection.
     * @param newer The newer collection.
     * @param finder The class used to determine if a collection contains an element.
     * @param <T>
     * @return
     */
    public static <T> Result<T> compareAnyOrder(Collection<T> older, Collection<T> newer, CollectionFinder<T> finder) {
        if( older == null && newer == null ) {
            return new Result<>(Collections.emptyList(),Collections.emptyList());
        } else if( older == null ) {
            return new Result<>(newer,Collections.emptyList());
        } else if( newer == null ) {
            return new Result<>(Collections.emptyList(),older);
        } else {
            Collection<T> added = new ArrayList<>();
            Collection<T> removed = new ArrayList<>();
            for( T o : older ) {
                if( ! finder.contains( newer , o ) ) {
                    removed.add( o );
                }
            }
            for( T o : newer ) {
                if( ! finder.contains( older , o ) ) {
                    added.add( o );
                }
            }
            return new Result<>(added,removed);
        }
    }

}