Question

我最近一直试图通过点击按钮开发一个代码，以便在JTable中将两列数据相乘。按钮单击操作中的代码如下：

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”按钮根据N值添加微调框中的行数：

enter image description here

按钮执行上述代码。在运行应用程序时，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)

任何人都可以请更正我的代码或告诉我如何将JTable中的数据乘以列数据的逻辑吗？

完整代码如下

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

生成按钮的ActionListener重复将null添加到TableModel，这会导致Double.parseDouble()投掷NullPointerException。至少要为您的模型添加可解析的值：

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

请问你能给我正确的代码吗？

所选值仅供参考;您可能希望从标识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绝对定位而选择合适的layout。

JTable中的数据乘以两列

1 个答案: