Arrays.sort(Comparator) 巧用

java 代码

/**
 * <p>
 * This method simply orders the ranked query result by date.
 * </p>
 *
 * @param result ranked result to be ordered
 *
 * @return ordered result
 *
 * @throws OrderException if the order execution fails because of some reason.
 */
public RankedQueryResult order(RankedQueryResult result) throws OrderException {
    SearcherHelper.checkNull(result, "result");

    // TreeMap(Key date, Value id) may be a choice to implement sort. But it has a problem. The
    // Date of two Documents may be equal. In that case, when put them into the Map,
    // one Document will be neglected and a bug is introduced.
    // Also, I tried Arrays.sort(rankedOrder,new Comparator(){}. But in this
    // case, we can not throw the DocumentRepositoryException from Document Repository in Comparator#compare.
    // What's more, every time it compares Date, it'll have to retrieve the Date from     // the repository.
    // Finally, I decided to implement it this way.

    /**
     * An Object for WordSourceId Date pair for the convenience of sorting WordSourceId by Date.
     */
    final class IdDateObject {
        /** The WordSourceId this object related */
        private WordSourceId id;

        /** The Date of the WordSourceId */
        private Date date;

        /**
         * Constructor for the project with the related WordSourceId and its date.
         *
         * @param id the WordSourceId this object related
         * @param date the Date of the WordSourceId
         */
        IdDateObject(WordSourceId id, Date date) {
            this.id = id;
            this.date = date;
        }

        /**
         * Returns the date of the WordSourceId.
         *
         * @return the date of the WordSourceId
         */
        Date getDate() {
            return date;
        }

        /**
         * Returns the WordSourceId the object related.
         *
         * @return the WordSourceId the object related
         */
        WordSourceId getId() {
            return id;
        }
    }// end for final class IdDateObject

    // constructs the IdDateObject array
    WordSourceId[] rankedOrder = result.getRankedOrder();
    IdDateObject[] idDateObjects = new IdDateObject[rankedOrder.length];
    for (int i = 0; i < rankedOrder.length; i++) {
        idDateObjects[i] = new IdDateObject(rankedOrder[i], getDocumentDate(rankedOrder[i]));
    }

    // sort in idDateObjects
    Arrays.sort(idDateObjects, new Comparator() {
        /**
         * Compares two IdDateObject objects according to the Date.
         * <p>
         *
         * <pre>
         *   If the local variable decreasing is true:
         *      If two objects' creation Dates are equal, 0 will be returned.
         *      If arg0 greater than arg1, a positive int is returned.
         *      Else a negative is returned.
         *   Else the local variable decreasing is false:
         *      If two objects' creation Dates, 0 will be returned.
         *      If arg0 greater than arg1, a negitive integer is returned.
         *      Else a positive integer is returned.
         * </pre>
         *
         * @param arg0 the first WordSourceId to compare
         * @param arg1 the second WordSourceId to compare
         * @return an integer representing the compare result according the above rule
         * @throws ClassCastException if the arguments' types prevent them from being compared by this Comparator.
         */
        public int compare(Object arg0, Object arg1) {
            IdDateObject object1 = (IdDateObject) arg0;
            IdDateObject object2 = (IdDateObject) arg1;
            Date date0 = object1.getDate();
            Date date1 = object2.getDate();

            int result = date0.compareTo(date1);
            if (decreasing) {
                result *= -1;
            }
            return result;
        }

    });

    // retrieve sort result
    WordSourceId[] resultOrder = new WordSourceId[rankedOrder.length];
    for (int i = 0; i < idDateObjects.length; i++) {
        resultOrder[i] = idDateObjects[i].getId();
    }
    // create and return a new ranked query result ordered by date
    return new RankedQueryResult(result.getResult(), result.getAllRelevances(), resultOrder);
}