A custom implementation of CursorJoiner. Allows you to compare int type. Also configures order.

gistfile1.txt

/**
 * Custom implementation of {@Link android.database.CursorJoiner.java}
 * Does a join on two cursors using specific columns. This class allows join by int type.
 * Tomoaki Imai 2016
 * reference: http://poly.hatenablog.com/entry/20101006/p1 
 * MIT License
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
public class CustomCursorJoiner
        implements Iterator<CustomCursorJoiner.Result>, Iterable<CustomCursorJoiner.Result> {
    private Cursor mCursorLeft;
    private Cursor mCursorRight;
    private boolean mCompareResultIsValid;
    private Result mCompareResult;
    private int[] mColumnsLeft;
    private int[] mColumnsRight;
    private String[] mStringValues;
    private int[] mIntValues;
    private JoinColumnType mType;
    private static OrderType sOrderType;

    /**
     * The result of a call to next().
     */
    public enum Result {
        /** The row currently pointed to by the left cursor is unique */
        RIGHT,
        /** The row currently pointed to by the right cursor is unique */
        LEFT,
        /** The rows pointed to by both cursors are the same */
        BOTH
    }

    /**
     * The type of column to join
     */
    public enum JoinColumnType {
        STRING,
        INT
    }

    /**
     * Order
     */
    public enum OrderType {
        ASC, DESC;
    }

    /**
     * Initializes the CursorJoiner and resets the cursors to the first row. The left and right
     * column name arrays must have the same number of columns.
     * @param cursorLeft The left cursor to compare
     * @param columnNamesLeft The column names to compare from the left cursor
     * @param cursorRight The right cursor to compare
     * @param columnNamesRight The column names to compare from the right cursor
     * @param type the type of columns to compare
     * @param orderType the columns order (ASC or DESC)
     */
    public CustomCursorJoiner(
            Cursor cursorLeft, String[] columnNamesLeft,
            Cursor cursorRight, String[] columnNamesRight, JoinColumnType type, OrderType orderType) {
        if (columnNamesLeft.length != columnNamesRight.length) {
            throw new IllegalArgumentException(
                    "you must have the same number of columns on the left and right, "
                            + columnNamesLeft.length + " != " + columnNamesRight.length);
        }

        mCursorLeft = cursorLeft;
        mCursorRight = cursorRight;

        mCursorLeft.moveToFirst();
        mCursorRight.moveToFirst();

        mCompareResultIsValid = false;

        mColumnsLeft = buildColumnIndiciesArray(cursorLeft, columnNamesLeft);
        mColumnsRight = buildColumnIndiciesArray(cursorRight, columnNamesRight);

        mType = type;
        switch (mType) {
            case STRING:
                mStringValues = new String[mColumnsLeft.length * 2];
                break;
            case INT:
                mIntValues = new int[mColumnsLeft.length * 2];
        }
        
        sOrderType = orderType;
    }

    public Iterator<Result> iterator() {
        return this;
    }

    /**
     * Lookup the indicies of the each column name and return them in an array.
     * @param cursor the cursor that contains the columns
     * @param columnNames the array of names to lookup
     * @return an array of column indices
     */
    private int[] buildColumnIndiciesArray(Cursor cursor, String[] columnNames) {
        int[] columns = new int[columnNames.length];
        for (int i = 0; i < columnNames.length; i++) {
            columns[i] = cursor.getColumnIndexOrThrow(columnNames[i]);
        }
        return columns;
    }

    /**
     * Returns whether or not there are more rows to compare using next().
     * @return true if there are more rows to compare
     */
    public boolean hasNext() {
        if (mCompareResultIsValid) {
            switch (mCompareResult) {
                case BOTH:
                    return !mCursorLeft.isLast() || !mCursorRight.isLast();

                case LEFT:
                    return !mCursorLeft.isLast() || !mCursorRight.isAfterLast();

                case RIGHT:
                    return !mCursorLeft.isAfterLast() || !mCursorRight.isLast();

                default:
                    throw new IllegalStateException("bad value for mCompareResult, "
                            + mCompareResult);
            }
        } else {
            return !mCursorLeft.isAfterLast() || !mCursorRight.isAfterLast();
        }
    }

    /**
     * Returns the comparison result of the next row from each cursor. If one cursor
     * has no more rows but the other does then subsequent calls to this will indicate that
     * the remaining rows are unique.
     * <p>
     * The caller must check that hasNext() returns true before calling this.
     * <p>
     * Once next() has been called the cursors specified in the result of the call to
     * next() are guaranteed to point to the row that was indicated. Reading values
     * from the cursor that was not indicated in the call to next() will result in
     * undefined behavior.
     * @return LEFT, if the row pointed to by the left cursor is unique, RIGHT
     *   if the row pointed to by the right cursor is unique, BOTH if the rows in both
     *   cursors are the same.
     */
    public Result next() {
        if (!hasNext()) {
            throw new IllegalStateException("you must only call next() when hasNext() is true");
        }
        incrementCursors();
        assert hasNext();

        boolean hasLeft = !mCursorLeft.isAfterLast();
        boolean hasRight = !mCursorRight.isAfterLast();

        if (hasLeft && hasRight) {
            int compareResult = 0;
            switch (mType){
                case STRING:
                    populateStringValues(mStringValues, mCursorLeft, mColumnsLeft, 0 /* start filling at index 0 */);
                    populateStringValues(mStringValues, mCursorRight, mColumnsRight, 1 /* start filling at index 1 */);
                    compareResult = compareStrings(mStringValues);
                    break;
                case INT:
                    populateIntValues(mIntValues, mCursorLeft, mColumnsLeft, 0 /* start filling at index 0 */);
                    populateIntValues(mIntValues, mCursorRight, mColumnsRight, 1 /* start filling at index 1 */);
                    compareResult = compareInts(mIntValues);
                    break;
                default:
                    populateStringValues(mStringValues, mCursorLeft, mColumnsLeft, 0 /* start filling at index 0 */);
                    populateStringValues(mStringValues, mCursorRight, mColumnsRight, 1 /* start filling at index 1 */);
                    compareResult = compareStrings(mStringValues);
                    break;
            }

            switch (compareResult) {
                case -1:
                    mCompareResult = Result.LEFT;
                    break;
                case 0:
                    mCompareResult = Result.BOTH;
                    break;
                case 1:
                    mCompareResult = Result.RIGHT;
                    break;
            }
        } else if (hasLeft) {
            mCompareResult = Result.LEFT;
        } else  {
            assert hasRight;
            mCompareResult = Result.RIGHT;
        }
        mCompareResultIsValid = true;
        return mCompareResult;
    }

    public void remove() {
        throw new UnsupportedOperationException("not implemented");
    }

    /**
     * Reads the strings from the cursor that are specifed in the columnIndicies
     * array and saves them in values beginning at startingIndex, skipping a slot
     * for each value. If columnIndicies has length 3 and startingIndex is 1, the
     * values will be stored in slots 1, 3, and 5.
     * @param values the String[] to populate
     * @param cursor the cursor from which to read
     * @param columnIndicies the indicies of the values to read from the cursor
     * @param startingIndex the slot in which to start storing values, and must be either 0 or 1.
     */
    private static void populateStringValues(String[] values, Cursor cursor, int[] columnIndicies,
                                       int startingIndex) {
        assert startingIndex == 0 || startingIndex == 1;
        for (int i = 0; i < columnIndicies.length; i++) {
            values[startingIndex + i*2] = cursor.getString(columnIndicies[i]);
        }
    }

    /**
     * Reads the strings from the cursor that are specifed in the columnIndicies
     * array and saves them in values beginning at startingIndex, skipping a slot
     * for each value. If columnIndicies has length 3 and startingIndex is 1, the
     * values will be stored in slots 1, 3, and 5.
     * @param values the int[] to populate
     * @param cursor the cursor from which to read
     * @param columnIndicies the indicies of the values to read from the cursor
     * @param startingIndex the slot in which to start storing values, and must be either 0 or 1.
     */
    private static void populateIntValues(int[] values, Cursor cursor, int[] columnIndicies,
                                       int startingIndex) {
        assert startingIndex == 0 || startingIndex == 1;
        for (int i = 0; i < columnIndicies.length; i++) {
            values[startingIndex + i*2] = cursor.getInt(columnIndicies[i]);
        }
    }

    /**
     * Increment the cursors past the rows indicated in the most recent call to next().
     * This will only have an affect once per call to next().
     */
    private void incrementCursors() {
        if (mCompareResultIsValid) {
            switch (mCompareResult) {
                case LEFT:
                    mCursorLeft.moveToNext();
                    break;
                case RIGHT:
                    mCursorRight.moveToNext();
                    break;
                case BOTH:
                    mCursorLeft.moveToNext();
                    mCursorRight.moveToNext();
                    break;
            }
            mCompareResultIsValid = false;
        }
    }

    /**
     * Compare the values. Values contains n pairs of strings. If all the pairs of strings match
     * then returns 0. Otherwise returns the comparison result of the first non-matching pair
     * of values, -1 if the first of the pair is less than the second of the pair or 1 if it
     * is greater.
     * @param values the n pairs of values to compare
     * @return -1, 0, or 1 as described above.
     */
    private static int compareStrings(String... values) {
        if ((values.length % 2) != 0) {
            throw new IllegalArgumentException("you must specify an even number of values");
        }

        for (int index = 0; index < values.length; index+=2) {
            if (values[index] == null) {
                if (values[index+1] == null) continue;
                return -1;
            }

            if (values[index+1] == null) {
                return 1;
            }

            int comp = values[index].compareTo(values[index+1]);
            if (comp != 0) {
                return comp < 0 ? -1 : 1;
            }
        }

        return 0;
    }

    private static int compareInts(int... values) {
        if ((values.length % 2) != 0) {
            throw new IllegalArgumentException("you must specify an even number of values");
        }

        for (int index = 0; index < values.length; index += 2) {
            int comp = values[index] - values[index + 1];
            if (comp != 0) {
                if (sOrderType == OrderType.DESC) {
                    // if LEFT is smaller than RIGHT, move RIGHT cursor since value order is desc
                    return comp < 0 ? 1 : -1;
                } else if (sOrderType == OrderType.ASC) {
                    return comp > 0 ? 1 : -1;
                }
            }
        }
        return 0;
    }
}