JFreeChart - How do I color code multiple rows in a StackedBarRenderer?

Question

I am working on a program that takes an array of doubles and displays them all in one line on a horizontal bar graph. Right now it works except for the coloring. I have an indeterminate amount of rows so the data is added to the graph like this:

public CategoryDataset createDataset() {
    DefaultCategoryDataset bardataset1 = new DefaultCategoryDataset();
    for (int i = 0; i < nanoArray.length; i++) {
        bardataset1.addValue(nanoArray[i], "Packet" + i, "Class A");
        bardataset1.addValue(startgap, "Packet Gap" + i, "Class A");
    }
}

This stacks the data properly but because there are around 300 different rowKeys it assigns 300 different colors. I attached this picture to show you what it looks like:

http://i.imgur.com/hg33P.png

As you can see this makes the data completely unreadable. What I want is to see bars of alternating colors of red then blue.

Edit: I have found the answer; I used jcern's method. I also wrote a for loop that iterates through the length of my double array and assigns a color based on whether it is even or odd.

for (int i = 0; i < packetCount; i++) {
        setSeriesToolTipGenerator(i, new StandardCategoryToolTipGenerator());
        if (i % 2 == 0) {
            setSeriesPaint(i, new Color(255, 0, 0));
        } else {
            setSeriesPaint(i, new Color(0, 0, 0));
        }
    }

Answer 1

You need to create a new renderer and specify that to the plot.

First, you'll create a render that has the two colors you want:

CategoryItemRenderer renderer = new StackedBarRenderer {
     private Paint[] colors = new Paint[] {
        new Color(255, 0, 0), 
        new Color(0, 0, 255)
     }

     public Paint getSeriesPaint(int series) {
       return colors[(series % 2)];
     }
};

Then, grab the plot and specify which render you want to use:

if(chart.getPlot() instanceof CategoryPlot){
  chart.getCategoryPlot().setRenderer(renderer);
}

Hopefully, that should get you where you want to be.