complete blank date fields based on last date in cell above

I have a spreadsheet full of records, in column A is a date, however, not every row of data is full of date entries, when it should. What I need to do is pre-populate the dates, basically if the cell has no date value, it should be populated with the date immediately above (or not in the cell above, the one aboive that), this rule only counts until the next cell in the column with a date in, and then the same process applies.

 i.e some sample data below.I would ideally like to create a "date 2" column in column B so I can view the 2 side by side to ensure it has worked properly.

A1 - 12/08/2015
A2 - (empty)
A3 - (empty)
A4 - 21/08/2015
A5 - (empty)
A6 (27/08/2015
A7 (empty)

In the example above, A2 and A3 would need to be populated with 12/08/2015 (as the date in A1), A5 would need to be populated with 21/08/2015 (as thats the last date shown in A4), A7 would need to be populated with 27/08/2015 (as thats the last date shown in A7). How can this be achieved in excel, can you provide any pointers?