One of the classes in the plot package, EditablePlot, extends the Plot class with a facility for graphically editing the data being plotted. The following plot is editable:
At the bottom, you can select one of the three data sets. Then, by dragging the right mouse button, you can change the values plotted for the corresponding data set.
This demonstration is implementing using the EditablePlotMLApplet class in the ptolemy.plot.plotml package. That applet has an applet parameter, dataurl, that specifies the initial data to be plotted and the format information (the fact that it is a bar graph, the title, the axis labels, etc.). It creates the choice menu at the bottom and implements the plot using the EditablePlot class instead of the base class Plot.