Given a DataFrame storesDF with an integer column openDate representing UNIX epoch timestamps, which code snippet correctly converts these timestamps to a string representation using Java's SimpleDateFormat?

The DataFrame structure is as follows:

storeId  openDate
0        1100746394
1        1474410343
2        1116610009
3        1180035265
4        1408024997

Fill in the blanks in the following code block to achieve this conversion:

storesDF.__1__("openDateString", __2__(__3__, __4__))