Calculating column value in current row of Spark Dataframe based on the calculated value of a column in previous row using java

Question

Let's say I have static value as 10000

Now, I have a Dataframe like below

Col A	Col B
A	500
S	100
A	1000
S	100

With Transformation I want it like below

Col A	Col B	Col C
A	500	10500
S	100	10400
A	1000	11400
S	100	11300

The thing works by the details provided below

• For the first row based on Col A value (A for add and S for subtract) I am adding value Col B value with static value to get Col C value

• From next row onward based on Col A value I am adding or subtracting Col B value with Col C value of previous row.

I was trying to find out Col A value using spark functions class but haven't found anything. Please help me to form the logic.