jForex documentation is huge, technically correct, but it is absolutely useless to understand some basic things from scratch. Here's a simple problem in simple indicator: the input - two sources Ask and Bid, output graph - average price of bar's High and Low. I guess that calcultae is called for each source separately, but why debug printing for the first source of startindex and endindex is correct but for the second - is not? How do I understand for which of the sources calculate is called when it calulated? What is wrong with this code?
I would be grateful for any help, especially for the links (except dukascopy wiki) where in normal words described basic objects of jForex, how do they intaeracts one with another and in what sequence.

What do you mean by "correct"? What do you find being incorrect and what the values should be instead?
Please elaborate.

as I expected, I have 2 input and each of them must have some data. in method calculate I print its start and end indexes values. in first call (for the 1-st input??) i get 0 3999 and in a second call (for the second input??) - 0 0. When I print last known time for bouth inputs, I got different values, with difference in a days!!
So, in my code I have 2 inputs. I want to know for which of one of them was called method calculate and why start and end indexes is different for them.

This is by design - the platform passes as many inputs as it finds necessary. This is not the "first"/"second" input, but both at the time - the calculate call which by default happens on every tick or when there is a change on chart. You can determine minimum input count that you receive by increasing the getLookback value, see:
https://www.dukascopy.com/wiki/#IIndicator_interface/Method_getLookback
If you receive input values for the last 4000 candles on chart then depending on period it could even be months of years.
You need to calcuate both outputs in the same calculate call. You can use as an example for multi-output indicator the AwesomeOscillator indicator and for multi-input - the ForceIndicator, see:
https://www.dukascopy.com/wiki/#Platform_indicator_source_files

I see.... but in my exaple this 2 inputs is Ask and Bid IBars for the same period of the same chart. difference for a seconds I can understand... but days on ticks - unbelivable
There is some error in my source code or may be in my understanding of basic mechanism how platform is realy working is wrong.
Is there any document, where I can read words like "after recieving new tick, new data stored will be in AAAA array, then platform calling method BBBBB, which must return CCCCC result...."

The documentation is javadocs and wiki. For example indicators see the platform indicator sources and the forum Code Base/Indicators. To better understand how the indicator works - input, output sizes, lookback, indices, etc. - conisder adding additional logging statements in the calculate method, for example as it is done in the HolderTestLog.java example here:
viewtopic.php?f=65&t=48828&p=69618

thanks a lot, but... "study by example" is works fine in many, but not in all cases
just imagine that you said same words to the newbie trader - look like your boss is trading and trade youself just like him! What do you think will learn newbie? How to push buttons? - yes! Stable and profitable trading? - never. Examples of other people's codes will never replace proper documentation. Unfortunately your wiki - is a reference book (some kind list) of the objects and their methods, but not a documentation how to use them together.
Ok. I will try to learn something by myself...

P.S. There was useless thread. I do not mind if you delete it.

ZENcoder,
The path has been shown.
It is YOU, who has to walk on it.

Please use https://www.dukascopy.com/swiss/english/forex/Visual/features/