You might have a look at org.jfree.chart.demo.TimeSeriesChartDemo1, and the associated API documentation. A typical command to run the demo might look like this:
java -cp lib/jfreechart-1.0.13.jar:lib/jcommon-1.0.16.jar \
org.jfree.chart.demo.TimeSeriesChartDemo1
The example uses org.jfree.data.time.Month to represent monthly data, but other units are available in org.jfree.data.time. See also the approach shown in this related example, which is based on TimeSeriesChartDemo1.