通过JTable中的数据乘以两列

Question

我最近试图通过单击按钮来开发在JTable中乘以两列数据的代码。按钮点击动作中的代码如下：

for (int i=0;i<model.getRowCount();i++){ 
    Double d= Double.parseDouble((String) model2.getValueAt(i,1)); 
    Double d2= Double.parseDouble((String) model3.getValueAt(i,2)); 
    Double d3=d*d2; 
    model.setValueAt(d3,i,3); 
} 

生成按钮增加了行数从基于N值微调框：

的按钮执行上面的代码。运行应用程序时，我收到以下错误和警告：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1838) 
    at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110) 
    at java.lang.Double.parseDouble(Double.java:538) 
    at mU$4.actionPerformed(mU.java:133) 
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022) 
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348) 
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) 
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) 
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252) 
    at java.awt.Component.processMouseEvent(Component.java:6535) 
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324) 
    at java.awt.Component.processEvent(Component.java:6300) 
    at java.awt.Container.processEvent(Container.java:2236) 
    at java.awt.Component.dispatchEventImpl(Component.java:4891) 
    at java.awt.Container.dispatchEventImpl(Container.java:2294) 
    at java.awt.Component.dispatchEvent(Component.java:4713) 
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888) 
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525) 
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466) 
    at java.awt.Container.dispatchEventImpl(Container.java:2280) 
    at java.awt.Window.dispatchEventImpl(Window.java:2750) 
    at java.awt.Component.dispatchEvent(Component.java:4713) 
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758) 
    at java.awt.EventQueue.access$500(EventQueue.java:97) 
    at java.awt.EventQueue$3.run(EventQueue.java:709) 
    at java.awt.EventQueue$3.run(EventQueue.java:703) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86) 
    at java.awt.EventQueue$4.run(EventQueue.java:731) 
    at java.awt.EventQueue$4.run(EventQueue.java:729) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76) 
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728) 
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201) 
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116) 
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105) 
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) 
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93) 
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82) 

谁能请纠正我的代码或告诉我的逻辑如何通过列数据乘以在JTable的数据？

完整的代码如下

import java.awt.EventQueue; 

import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.border.EmptyBorder; 
import javax.swing.JLabel; 
import javax.swing.JSpinner; 
import javax.swing.JButton; 
import javax.swing.JTable; 
import javax.swing.JScrollPane; 
import javax.swing.table.DefaultTableModel; 
import javax.swing.JTextField; 
import javax.swing.UIManager; 

import java.awt.event.ActionListener; 
import java.util.ArrayList; 
import java.util.Arrays; 
import java.util.List; 
import java.util.Vector; 
import java.awt.event.ActionEvent; 
import javax.swing.JTextArea; 

public class mU extends JFrame { 

    private JPanel contentPane; 
    private JTable table; 
    private JTextField textField; 
    Double l2; 
    Double l4; 
    Double d,d2; 
    int hu; 
    /** 
    * Launch the application. 
    */ 
    public static void main(String[] args) { 
     EventQueue.invokeLater(new Runnable() { 
      public void run() { 
       try { 
        mU frame = new mU(); 
        frame.setVisible(true); 
       } catch (Exception e) { 
        e.printStackTrace(); 
       } 
      } 
     }); 
    } 

    /** 
    * Create the frame. 
    */ 
    public mU() { 
     try{  
      UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel"); 
     } 
     catch(Exception w1){ 

     } 

     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     setBounds(100, 100, 486, 297); 
     contentPane = new JPanel(); 
     contentPane.setBorder(new EmptyBorder(5, 5, 5, 5)); 
     setContentPane(contentPane); 
     contentPane.setLayout(null); 

     JLabel lblNumberOfMachines = new JLabel("Number of Machines"); 
     lblNumberOfMachines.setBounds(10, 11, 120, 14); 
     contentPane.add(lblNumberOfMachines); 

     JSpinner spinner = new JSpinner(); 
     spinner.setBounds(140, 8, 48, 20); 
     contentPane.add(spinner); 

     JScrollPane scrollPane = new JScrollPane(); 
     scrollPane.setBounds(208, 11, 252, 239); 
     contentPane.add(scrollPane); 

     table = new JTable(); 
     table.setRowSelectionAllowed(false); 
     table.setModel(new DefaultTableModel(
      new Object[][] { 
      }, 
      new String[] { 
       "Machine", "N(1)", "N(0)", "Qan" 
      } 
     )); 
     scrollPane.setViewportView(table); 
     DefaultTableModel model = (DefaultTableModel) table.getModel(); 
     table.setModel(model); 

     JLabel lblSum = new JLabel("Sum"); 
     lblSum.setBounds(10, 117, 46, 14); 
     contentPane.add(lblSum); 

     textField = new JTextField(); 
     textField.setBounds(39, 114, 105, 20); 
     contentPane.add(textField); 
     textField.setColumns(10); 

     JButton btnNewButton = new JButton("Generate"); 
     btnNewButton.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent e) { 
       DefaultTableModel model = (DefaultTableModel) table.getModel(); 
       table.setModel(model); 
       int hu=(Integer) spinner.getValue(); 
       for(int i=0;i<hu;i++) { 
        model.addRow(new Object[] {"M"+(i+1),null,null,null}); 

       } 
      } 
     }); 

     btnNewButton.setBounds(10, 36, 77, 23); 
     contentPane.add(btnNewButton); 


     JButton btnClear = new JButton("CLEAR"); 
     btnClear.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent e) { 
       model.setRowCount(0); 
      } 
     }); 
     btnClear.setBounds(89, 36, 65, 23); 
     contentPane.add(btnClear); 

     JButton btnInitilize = new JButton("N"); 
     btnInitilize.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent e) { 

       for (int i = 0; i <model.getRowCount(); i++) { 
        Double d= Double.parseDouble((String) model.getValueAt(i,1)); 
        Double d2= Double.parseDouble((String) model.getValueAt(i,2)); 
        Double d3=d*d2; 
        model.setValueAt(d3,i,3); 
       } 

      } 
     }); 
     btnInitilize.setBounds(10, 63, 46, 23); 
     contentPane.add(btnInitilize); 










    } 
} 

Answer 1

的ActionListener您生成按钮反复增加null到TableModel，这将导致Double.parseDouble()扔NullPointerException。至少，添加可解析值模型：

for (int i = 0; i < hu; i++) { 
    String s = String.valueOf(i); 
    model.addRow(new Object[] {"M" + s, s, "42", ""}); 
} 

可以放下我正确的代码吗？

选定的值是为了说明;您可能希望从身份元素的字符串表示开始，例如"0"：

model.addRow(new Object[] {"M" + s, "0", "0", ""}); 

顺便说一句，截图说明了为什么你应该避免在赞成适当layout绝对定位。