Graph tool/lib for Java

I want to be able to create more dynamic linear graphs with the following:
-Possibility to have more than one unit on the Y-axis at the same time as X is time.
-Possibility to have uneven lines in the graph. With uneven I mean that the different lines might have points registered on different X-values than each other and not with even intervalls, for instance:

Line 1 might have points: (22.4,44) (39.0,55)  (42.7,113.5) ...
Line 2 might have points: (2,1000) (3.2,1200)  (4.0,1500) (4.3,1500) (6.3,3400) ... (43.2,800)

What would be a good way to create it? Do you have any fitting libs?

Anything working with JavaFx would be nice. Also something without charge or with the possibility to use for free for non-commercial development.
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I've done graphs before using D3.js (a javascript data visualisation library). I fed the data into it in Json format.

I know some people have also used jfreechart.

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