The same as AJ said, but with a few more words on J K flip flops
Two outputs Q and Qbar, They are just inverts of each other, and they are never indeterminate ie they always have a value.
Two main inputs J and K with a third input, the clock.
In normal operation the clock input is significant as it is used as a trigger to evaluate for change. When the clock input goes from 0 to 1 the evaluation of inputs and determination of outputs is done. This is significant, if you cut off the clock signal no change to outputs will occur. eg stick the clock signal through an AND gate with an enable signal to turn the whole thing on / off as desired.
If J and K are both low when clock goes up then there is no change to Q (and off course Qbar)
If J and K are both hi when clock goes up then there is a toggle change to Q ie it changes state from what it previously was
If J and K are different when clock goes up then then Q takes the value of J
Normally also has a Preset and Clear input that drive Q to either 0 or 1, irrespective of J, K and more importantly the clock
With all these words to explain, we see why the idea of truth tables came about!
