Have aggregate function group results in one row

I have a table that has the following columns:

• debit
• credit
• payment_method
• class

Now I will perform this query:

 select sum(debit - credit), payment_method, class 
 from my_table 
 group by payment_method, class 

And since I have various payment methods and various classes, I will have several rows of the result set.

Now I want to be able to aggregate this result and have the output grouped by class only, for example for a certain class 001 I want to have:
payment_method1, sumofpayment_method1, payment_method2, sumofpayment_method2, payment_method3, sumofpayment_method3 in one row.

Is it possible in Postgres 9.1?

Update:

The table definition is as follows:-

• debit numeric(10,2)
• credit numeric(10,2)
• payment_method varchar(20)
• class varchar(25)