JTable的revalidate有什么用,附属小学源码。

import java.awt.*;import java.awt.event.*;import java.util.Vector;import javax.swing.*;import javax.swing.event.*;import javax.swing.table.*;public class AddRemoveCells implements ActionListener{   JTable table = null;   DefaultTableModel defaultModel = null;   public AddRemoveCells(){      JFrame f = new JFrame();      String[] name = {"1","2","3","4","5"};      String[][] data = new String[5][5];      int value = 1;      for(int i=0;i<data.length;i++){         for(int j=0;j<data[i].length;j++)            data[i][j] = String.valueOf(value++);      }      defaultModel = new DefaultTableModel(data,name);      table = new JTable(defaultModel);      table.setPreferredScrollableViewportSize(new Dimension(400,80));      JScrollPane s = new JScrollPane(table);            JPanel panel = new JPanel();      JButton b = new JButton("增加列");      panel.add(b);      b.addActionListener(this);            JButton o = new JButton("删除行");      panel.add(o);      o.addActionListener(this);            b = new JButton("增加行");      panel.add(b);      b.addActionListener(this);      b = new JButton("删除列");      panel.add(b);      b.addActionListener(this);            Container contentPane = f.getContentPane();      contentPane.add(panel, BorderLayout.NORTH);      contentPane.add(s,BorderLayout.CENTER);            f.setTitle("AddR");      f.pack();      f.setVisible(true);      f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);   }   @SuppressWarnings("unchecked")   public void actionPerformed(ActionEvent e){      if(e.getActionCommand().equals("增加列"))         defaultModel.addColumn("增加列");      if(e.getActionCommand().equals("增加行"))         defaultModel.addRow(new Vector());      if(e.getActionCommand().equals("删除列")){         int columncount = defaultModel.getColumnCount()-1;         if(columncount >=0){            TableColumnModel columnModel = table.getColumnModel();            TableColumn tableColumn = columnModel.getColumn(columncount);            columnModel.removeColumn(tableColumn);            defaultModel.setColumnCount(columncount);         }      }      if(e.getActionCommand().equals("删除行")){         int rowcount = defaultModel.getRowCount()-1;         if(rowcount >= 0){            defaultModel.removeRow(rowcount);            defaultModel.setRowCount(rowcount);         }             }     table.revalidate();  //这句好象没用到？？？？   }   public static void main(String args[]){      new AddRemoveCells();   }}