所以基本上要求是根据搜索查询从数据库中获取结果。结果显示在JTable中。结果应该有5列。 4列包含从数据库中获取的值。第5列应该有按钮。单击该按钮时，应显示一个弹出窗口。现在搜索功能正常。当我需要在第5列显示按钮时，我收到错误。我用Google搜索并发现它可以通过TablCellRenderer完成。我也在我的代码中引用了相同的代码，引用此link现在，我收到错误
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at r_search_2$JTableButtonRenderer.getTableCellRendererComponent(r_search_2.java:193)
位于此块中： -
else
{
button.setForeground(table.getForeground());
button.setBackground(UIManager.getColor("Button.background"));
}
如果我从代码中删除此块，则搜索查询运行正常，但第5列中不显示按钮。那么错误在哪里，我该如何纠正？谢谢！
import java.awt.*;
import java.awt.event.*;
import java.io.File;
import java.sql.*;
import java.util.Vector;
import javax.swing.*;
import javax.swing.table.DefaultTableModel;
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.UIManager;
import javax.swing.table.AbstractTableModel;
import javax.swing.table.TableCellRenderer;
public class r_search_2 extends JFrame implements ActionListener
{
JFrame frame1;
JLabel l0, l1, l2;
JComboBox c1;
JButton b1;
Connection con;
ResultSet rs, rs1;
Statement st, st1;
PreparedStatement pst;
String ids;
static JTable table = new JTable(new JTableModel());
// static JTable table = new JTable();
String[] columnNames = {"SECTION NAME", "REPORT NAME", "CONTACT", "LINK","METRICS"};
String from;
Vector v = new Vector();
JMenuBar menu = new JMenuBar();
JPanel mainPanel = new JPanel(new BorderLayout());
JPanel topPanel = new JPanel(new FlowLayout(SwingConstants.LEADING, 60,25));
JScrollPane scroll = new JScrollPane(table);
r_search_2()
{
l1 = new JLabel("Search");
b1 = new JButton("submit");
l1.setBounds(75, 110, 75, 20);
b1.setBounds(150, 150, 150, 20);
b1.addActionListener(this);
topPanel.add(l1,BorderLayout.LINE_START);
try
{
File dbFile = new File("executive_db.accdb");
String path = dbFile.getAbsolutePath();
con = DriverManager.getConnection("jdbc:odbc:Driver={Microsoft Access Driver (*.mdb, *.accdb)}; DBQ= " + path);
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
st = con.createStatement();
rs = st.executeQuery("select index_name from Index1");
while (rs.next())
{
ids = rs.getString(1);
v.add(ids);
}
c1 = new JComboBox(v);
c1.setEditable(true);c1.setSelectedItem("");
c1.setBounds(150, 110, 150, 20);
topPanel.add(c1,BorderLayout.CENTER);
topPanel.add(b1,BorderLayout.LINE_END);
mainPanel.add(topPanel, BorderLayout.PAGE_START);
st.close();
rs.close();
}
catch (Exception e)
{
}
// setVisible(true);
}
public void actionPerformed(ActionEvent ae)
{
if (ae.getSource() == b1)
{
showTableData();
}
}
public void showTableData()
{
DefaultTableModel model = new DefaultTableModel();
model.setColumnIdentifiers(columnNames);
table.setModel(model);
table.setAutoResizeMode(JTable.AUTO_RESIZE_ALL_COLUMNS);
table.setFillsViewportHeight(true);
scroll.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
scroll.setVerticalScrollBarPolicy( JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);
from = (String) c1.getSelectedItem();
TableCellRenderer buttonRenderer = new JTableButtonRenderer();
table.getColumn("METRICS").setCellRenderer(buttonRenderer);
//System.out.println(table.getColumn("METRICS"));
//table.getColumn("Button2").setCellRenderer(buttonRenderer);
table.addMouseListener(new JTableButtonMouseListener(table));
String section_name = "";
String report_name = "";
String contact_name = "";
String link = "";
try
{
pst = con.prepareStatement("select distinct Section.Section_Name,Report.Report_Name,Report.Link,Contact.Contact_Name "
+ "FROM (( Section INNER JOIN Report ON Report.Section_ID=Section.Section_ID ) INNER JOIN Contact ON Contact.Contact_ID=Report.Contact_ID ) LEFT JOIN Metrics ON Metrics.Report_ID=Report.Report_ID "
+ " WHERE Section.Section_Name LIKE '%"+from+"%' OR Report.Report_Name LIKE '%"+from+"%' OR Metrics.Metric_Name LIKE '%"+from+"%' OR Contact.Contact_Name LIKE '%"+from+"%' ");
ResultSet rs = pst.executeQuery();
int i = 0;
while (rs.next()) {
section_name = rs.getString("Section_Name");
report_name = rs.getString("Report_Name");
contact_name = rs.getString("Contact_Name");
link = rs.getString("Link");
// String m="apple";
model.addRow(new Object[]{section_name, report_name, contact_name, link});
i++;
}
if (i < 1)
{
JOptionPane.showMessageDialog(null, "No Record Found", "Error", JOptionPane.ERROR_MESSAGE);
}
if (i == 1)
{
System.out.println(i + " Record Found");
} else {
System.out.println(i + " Records Found");
}
}
catch (Exception ex)
{
JOptionPane.showMessageDialog(null, ex.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
}
mainPanel.add(scroll);
mainPanel.revalidate();
mainPanel.repaint();
}
private static class JTableButtonRenderer implements TableCellRenderer
{
@Override public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected, boolean hasFocus, int row, int column) {
JButton button = (JButton)value;
if (isSelected) {
button.setForeground(table.getSelectionForeground());
button.setBackground(table.getSelectionBackground());
}
else
{
button.setForeground(table.getForeground());
button.setBackground(UIManager.getColor("Button.background"));
}
return button;
}
}
private static class JTableButtonMouseListener extends MouseAdapter
{
private final JTable table;
public JTableButtonMouseListener(JTable table)
{
this.table = table;
}
public void mouseClicked(MouseEvent e)
{
int column = table.getColumnModel().getColumnIndexAtX(e.getX());
int row = e.getY()/table.getRowHeight();
if (row < table.getRowCount() && row >= 0 && column < table.getColumnCount() && column >= 0)
{
Object value = table.getValueAt(row, column);
if (value instanceof JButton)
{
((JButton)value).doClick();
}
}
}
}
public static class JTableModel extends AbstractTableModel
{
private static final long serialVersionUID = 1L;
//private static final String[] COLUMN_NAMES = new String[] {"Id", "Stuff", "METRICS"};
String[] columnNames = {"SECTION NAME", "REPORT NAME", "CONTACT", "LINK","METRICS"};
private static final Class<?>[] COLUMN_TYPES = new Class<?>[] {String.class, String.class,String.class, String.class, JButton.class};
@Override public int getColumnCount()
{
return columnNames.length;
}
@Override public int getRowCount()
{
return 4;
}
@Override public String getColumnName(int columnIndex)
{
return columnNames[columnIndex];
}
@Override public Class<?> getColumnClass(int columnIndex)
{
return COLUMN_TYPES[columnIndex];
}
@Override public Object getValueAt(final int rowIndex, final int columnIndex)
{
switch (columnIndex) {
case 0: //return rowIndex;
case 1: //return "Text for "+rowIndex;
case 2: // fall through
case 3: final JButton button = new JButton(columnNames[columnIndex]);
// button.setPreferredSize(new Dimension(100, 100));
button.setSize(new Dimension(10,10));
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
JOptionPane.showMessageDialog(JOptionPane.getFrameForComponent(button),
"Button clicked for row "+rowIndex);
}
});
return button;
default: return "";
}
}
}
public static void main(String args[])
{
r_search_2 s=new r_search_2();
//new r_search_2();
JFrame fr=new JFrame("Search Executive Reports");
//fr.add(s.getUI());
fr.add(s.mainPanel);
fr.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
fr.setLocationByPlatform(true);
fr.setSize(1000, 400);
//fr.pack();
fr.setVisible(true);
// new r_search_2();
}
}
答案 0 :(得分：1)
不要使用MouseListener;使用TableCellEditor，图示为here。方便的是，DefaultCellEditor可以作为弹出组件委托给JComboBox。
答案 1 :(得分：1)
JTableButtonRenderer
中的代码存在问题JButton button =（JButton）value;
最有可能＆＃34;价值＆＃34;在这里是null。 用于测试创建按钮为JButton按钮=新JButton（＆＃34;按钮＆＃34;）;
如果有效，请告诉我。