i defined a decision table on class object
rule flow should receive array of this class.
how should the Implementation Arguments of the task in rule flow be defined?
You need to define a loop with a counter in your ruleflow and in each cycle call the decision table task with the array member addressed by the counter and then increment the counter at the end of the loop. Take a look at ruleflow docs or simply add a loop to your flow and you should be able to see how associate a counter with it.
A better (in many cases) alternative would be to redesign the decision table so that it takes the whole array of objects as a paramete, define a pattern within the decision table and write conditions against that pattern as if it was a single object passed in.
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