[ Java 常見問題 ] JFreeChart: Apply a color to a single bar of single series graph

來源自 這裡 
Question: 
In my chart I only have one serie, and I would like -according to the value- to set a different color for the bar. For exemple : 

0-20 -> RED, 20-80 -> YELLOW, 80-100 -> GREEN

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1. CategoryPlot plot = chart.getCategoryPlot();  
2. CategoryDataset dataset = plot.getDataset(0);  
3.   
4. Number value = dataset.getValue(dataset.getRowKey(0), dataset.getColumnKey(0));  
5. Double val = value.doubleValue();  
6.   
7. if (val <= 20.0) {  
8.     BarRenderer renderer = (BarRenderer) plot.getRenderer();  
9.     Paint tmp = renderer.getItemPaint(row, column);  
10.   
11.     /* 
12.     ** Help Please 
13.     */        
14. }  
15.   
16. return chart;  

This is where I reached, I am then blocked and don't know really where to go. I saw in the documentation that Paint is an interface but none of the class implementing this interface does provide a setXXX() method. So my two question are : 
1. How do I set a color to a single Bar ? 
2. How do I apply that to my chart ? 

Answer: 
You'll need to create your own subclass of BarRenderer and override getItemPaint(). Instead of choosing a color based on column, choose it based on your value. Here's an outline to show how the existing BarRenderer works. 

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1. plot.setRenderer(new MyRender());  
2. ...  
3. class MyRender extends BarRenderer {  
4.   
5.     @Override  
6.     public Paint getItemPaint(int row, int col) {  
7.         System.out.println(row + " " + col + " " + super.getItemPaint(row, col));  
8.         return super.getItemPaint(row, col);  
9.     }  
10. }  

Example: 
底下範例將 Bar Chart 定義下面的數值範圍使用不同的顏色顯示: 

* <100: br="" green="" nbsp="">* 100~2xx: Yellow
* 3xx~4xx: Orange
* >499: Red

- BarChartDemo5.java 

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1. package charts.bar.category;  
2.   
3. import java.awt.Color;  
4. import java.awt.Dimension;  
5. import java.awt.Font;  
6. import java.awt.Paint;  
7. import java.util.ArrayList;  
8. import java.util.List;  
9.   
10. import javax.swing.JPanel;  
11.   
12. import org.jfree.chart.ChartFactory;  
13. import org.jfree.chart.ChartPanel;  
14. import org.jfree.chart.JFreeChart;  
15. import org.jfree.chart.axis.AxisLocation;  
16. import org.jfree.chart.axis.CategoryAxis;  
17. import org.jfree.chart.axis.NumberAxis;  
18. import org.jfree.chart.labels.StandardCategoryItemLabelGenerator;  
19. import org.jfree.chart.plot.CategoryPlot;  
20. import org.jfree.chart.plot.PlotOrientation;  
21. import org.jfree.chart.renderer.category.BarRenderer;  
22. import org.jfree.chart.title.TextTitle;  
23. import org.jfree.data.category.CategoryDataset;  
24. import org.jfree.data.category.DefaultCategoryDataset;  
25. import org.jfree.ui.ApplicationFrame;  
26. import org.jfree.ui.RefineryUtilities;  
27.   
28. // https://code.google.com/p/test-chart/source/browse/trunk/src/main/java/es/efor/plandifor/demo/BarChartDemo5.java?r=2  
29. public class BarChartDemo5 extends ApplicationFrame  
30. {  
31.     public static List Values = new ArrayList();  
32.     public BarChartDemo5(String s)  
33.     {  
34.             super(s);  
35.             JPanel jpanel = createDemoPanel();  
36.             jpanel.setPreferredSize(new Dimension(600, 400));  
37.             setContentPane(jpanel);  
38.     }  
39.   
40.     private static CategoryDataset createDataset()  
41.     {  
42.             DefaultCategoryDataset defaultcategorydataset = new DefaultCategoryDataset();  
43.             String s = "Prison Population Rates";  
44.             defaultcategorydataset.addValue(59D, s, "Norway"); Values.add(59D);  
45.             defaultcategorydataset.addValue(69D, s, "Switzerland"); Values.add(69D);  
46.             defaultcategorydataset.addValue(85D, s, "France"); Values.add(85D);  
47.             defaultcategorydataset.addValue(93D, s, "Syria"); Values.add(93D);  
48.             defaultcategorydataset.addValue(96D, s, "Germany"); Values.add(96D);  
49.             defaultcategorydataset.addValue(111D, s, "China"); Values.add(111D);  
50.             defaultcategorydataset.addValue(116D, s, "Australia"); Values.add(116D);  
51.             defaultcategorydataset.addValue(121D, s, "Egypt"); Values.add(121D);  
52.             defaultcategorydataset.addValue(129D, s, "England & Wales"); Values.add(129D);  
53.             defaultcategorydataset.addValue(157D, s, "New Zealand"); Values.add(157D);  
54.             defaultcategorydataset.addValue(205D, s, "Chile"); Values.add(205D);  
55.             defaultcategorydataset.addValue(229D, s, "Iran"); Values.add(229D);  
56.             defaultcategorydataset.addValue(359D, s, "Singapore"); Values.add(359D);  
57.             defaultcategorydataset.addValue(404D, s, "South Africa"); Values.add(404D);  
58.             defaultcategorydataset.addValue(406D, s, "Ukraine"); Values.add(406D);  
59.             defaultcategorydataset.addValue(686D, s, "USA"); Values.add(686D);  
60.             return defaultcategorydataset;  
61.     }  
62.   
63.       
64.     private static JFreeChart createChart(CategoryDataset categorydataset)  
65.     {  
66.             JFreeChart jfreechart = ChartFactory.createBarChart("Prison Population Rates - Selected Countries", "Country", "Prisoners Per 100,000 National Population", categorydataset, PlotOrientation.HORIZONTAL, true, true, false);  
67.             jfreechart.addSubtitle(new TextTitle("Source: http://www.homeoffice.gov.uk/rds/pdfs2/r188.pdf", new Font("Dialog", 2, 10)));  
68.             jfreechart.setBackgroundPaint(Color.white);  
69.             CategoryPlot categoryplot = (CategoryPlot)jfreechart.getPlot();  
70.             categoryplot.setBackgroundPaint(Color.lightGray);  
71.             categoryplot.setRangeGridlinePaint(Color.white);  
72.             categoryplot.setRangeAxisLocation(AxisLocation.BOTTOM_OR_LEFT);  
73.             MyRender barrenderer = new MyRender(Values);  
74.             //BarRenderer or = (BarRenderer)categoryplot.getRenderer();              
75.             categoryplot.setRenderer(barrenderer);  
76.             //barrenderer.setBaseItemLabelsVisible(true);  
77.             barrenderer.setBaseItemLabelGenerator(new StandardCategoryItemLabelGenerator());  
78.             CategoryAxis categoryaxis = categoryplot.getDomainAxis();  
79.             categoryaxis.setCategoryMargin(0.0D);  
80.             categoryaxis.setUpperMargin(0.02D);  
81.             categoryaxis.setLowerMargin(0.02D);  
82.             NumberAxis numberaxis = (NumberAxis)categoryplot.getRangeAxis();  
83.             numberaxis.setStandardTickUnits(NumberAxis.createIntegerTickUnits());  
84.             numberaxis.setUpperMargin(0.10000000000000001D);  
85.             return jfreechart;  
86.     }  
87.   
88.     public static JPanel createDemoPanel()  
89.     {  
90.             JFreeChart jfreechart = createChart(createDataset());  
91.             return new ChartPanel(jfreechart);  
92.     }  
93.   
94.     public static void main(String args[])  
95.     {  
96.             BarChartDemo5 barchartdemo5 = new BarChartDemo5("Bar Chart Demo 5");  
97.             barchartdemo5.pack();  
98.             RefineryUtilities.centerFrameOnScreen(barchartdemo5);  
99.             barchartdemo5.setVisible(true);  
100.     }  
101.       
102.     public static class MyRender extends BarRenderer {    
103.         List values;  
104.           
105.         public MyRender(List values){this.values = values;}  
106.             
107.         @Override    
108.         public Paint getItemPaint(int row, int col) {             
109.            double value = values.get(col);  
110.            int h = ((int)value)/100;  
111.            if(value<100) return Color.GREEN;  
112.            else if(h<3) return Color.yellow;  
113.            else if(h<5) return Color.orange;  
114.            else return Color.red;  
115.         }    
116.     }   
117. }  

執行結果: