Implemt the query() Method SQLit Content Provider

AppProvider.java

...
  public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
    String sortOrder) {
        // Get readable database
        SQLiteDatabase database = mDbHelper.getReadableDatabase();

        // This cursor will hold the result of the query
        Cursor cursor=null;

        // Figure out if the URI matcher can match the URI to a specific code
        int match = uriMatcher.match(uri);
        switch (match) {
        case WORDS_CODE:
        // For the PETS code, query the pets table directly with the given
        // projection, selection, selection arguments, and sort order. The cursor
        // could contain multiple rows of the pets table.
        // TODO: Perform database query on pets table
        break;
        case ID_WORD_CODE:
        // For the PET_ID code, extract out the ID from the URI.
        // For an example URI such as "content://com.example.android.pets/pets/3",
        // the selection will be "_id=?" and the selection argument will be a
        // String array containing the actual ID of 3 in this case.
        //
        // For every "?" in the selection, we need to have an element in the selection
        // arguments that will fill in the "?". Since we have 1 question mark in the
        // selection, we have 1 String in the selection arguments' String array.
        selection = Words._ID + "=?";
        selectionArgs = new String[] { String.valueOf(ContentUris.parseId(uri)) };

        // This will perform a query on the pets table where the _id equals 3 to return a
        // Cursor containing that row of the table.
        cursor = database.query(Words.TABLE_NAME, projection, selection, selectionArgs,
            null, null, sortOrder);
        break;
        default:
        throw new IllegalArgumentException("Cannot query unknown URI " + uri);
        }
        return cursor;
    }
  ...