Exception in thread "main" java.lang.NoClassDefFoundError: org/jfree/data/category/CategoryDataset

Question

I tried creating a simple BarChart using JFreeChart. The code seems have no problem until I run it. The error message i got:

Exception in thread "main" java.lang.NoClassDefFoundError: org/jfree/data/category/CategoryDataset
    at test.Main.main(Main.java:7)
Caused by: java.lang.ClassNotFoundException: org.jfree.data.category.CategoryDataset
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526)
    ... 1 more

Here's my code, given that I have a main class to call the ChartBar():

package chart;

import java.awt.BorderLayout;

import javax.swing.JFrame;

import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.CategoryPlot;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.data.category.CategoryDataset;
import org.jfree.data.category.DefaultCategoryDataset;

public class ChartBar extends JFrame{
    private DefaultCategoryDataset dataset;
    private JFreeChart chart;
    private CategoryPlot categoryPlot;
    private ChartPanel chartPanel;
    
    public ChartBar() {
        
        dataset = new DefaultCategoryDataset();
        dataset.addValue(200, "Viet Nam", "2000");
        
        //create chart
        chart = ChartFactory.createBarChart("T la chung m", "", "Ty do", dataset, PlotOrientation.VERTICAL, true, true, false);
                
        categoryPlot = chart.getCategoryPlot();
                
        chartPanel = new ChartPanel(chart);
        
        getContentPane().removeAll();
        getContentPane().add(chartPanel, BorderLayout.CENTER);
//      getContentPane().validate();
        
    }
}

I search up and do everything i can, I'm very sure I've included the library in classpath. And the JFreeChart is the latest version. I can even see the "CategoryDataset" class in my explorer....