关于jtable添加行的问题

import javax.swing.*;
import javax.swing.table.*;
import javax.swing.event.*;
import java.awt.*;

public class testq  extends JFrame
{
    int row;
    int column;
    Object[][] cells=    {{"001","zhang","88"},
            {"002","wang","90"},
            {"003","lin","99"},
            {"004","liao","60"},
            {"  "," "," "}
            };
    String[]    columnsName={"NO","Name","Score"};
    testq()
    {
        row=5;
        column=3;
        JTable table=new JTable(cells,columnsName);
        add(new JScrollPane(table),BorderLayout.CENTER);
        table.setModel(new TableModel());
    }
    
        public static void main(String[]args)
    {
        testq table=new testq();
        table.setVisible(true);
        table.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        table.setSize(500,500);
        
    }
    
    class TableModel extends DefaultTableModel
    {
        public TableModel()
        {
            addTableModelListener(new TableModelListener()
            {
                public void tableChanged(TableModelEvent e)
                {
                    if((String)getValueAt(e.getFirstRow(),e.getColumn())!=" ")
                    {
                        System.out.println(getRowCount());
                        Object[] object=new Object[]{" "," "," " };
                        addRow(object);
                    }
                }
            } );
        }
        public int getRowCount()
        {
            return row;
        }
        public int getColumnCount()
        {
            return column;
        }
        public Object getValueAt(int row ,int column)
        {
            return cells[row][column];
        }
        public String getColumnName(int c)
        {
            return columnsName[c];
        }
        public boolean isCellEditable(int row,int column)
        {
            return true;
        }    
    }
}



为什么每次运行时都会出现越界的异常？？？
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太花呢，看的不怎么懂，写电注释啊
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