Question

我在乘以单元格值后在setValue(...)中使用TableModelListener。没有.setValue，程序运行正常，但是，当它被添加时，似乎程序无限期地运行或者直到抛出异常。

以下是代码：

public void populateTable() {
    DefaultTableModel employeeModel = (DefaultTableModel) jTable1.getModel();
    employeeModel.addTableModelListener(new TableModelListener() {
        public void tableChanged(TableModelEvent e) {
            Integer totalDue = 0;
            Integer quantityValue = 0;
            Integer rateValue = 0;
            try {
                quantityValue = Integer.parseInt(employeeModel.getValueAt(0, 2).toString());
                rateValue = Integer.parseInt(employeeModel.getValueAt(0, 3).toString());
            } catch (NullPointerException f) {
            }
            totalDue = quantityValue * rateValue;
            System.out.println(totalDue);
            employeeModel.setValueAt(totalDue, 0, 4);
        }
    });
}

Answer 1

似乎程序无限期地运行

每次执行setValue(...)时，都会生成TableModelEvent。

TableModelListener中的代码会计算费用，然后会生成另一个setValue(...)，从而导致生成另一个TableModelEvent，并让您自己进入无限循环。

因此，在TableModelListener中，您需要添加对哪个列已更改的检查，并仅在值或数量发生更改时计算成本。

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

public class TableProcessing extends JPanel implements TableModelListener
{
    public TableProcessing()
    {
        String[] columnNames = {"Item", "Quantity", "Price", "Cost"};
        Object[][] data =
        {
            {"Bread", new Integer(1), new Double(1.11), new Double(1.11)},
            {"Milk", new Integer(1), new Double(2.22), new Double(2.22)},
            {"Tea", new Integer(1), new Double(3.33), new Double(3.33)},
            {"Cofee", new Integer(1), new Double(4.44), new Double(4.44)}
        };

        DefaultTableModel model = new DefaultTableModel(data, columnNames)
        {
            //  Returning the Class of each column will allow different
            //  renderers to be used based on Class
            @Override
            public Class getColumnClass(int column)
            {
                return getValueAt(0, column).getClass();
            }

            //  The Cost is not editable
            @Override
            public boolean isCellEditable(int row, int column)
            {
                return (column == 3) ? false : true;
            }
        };
        model.addTableModelListener( this );

        JTable table = new JTable( model );
        table.setPreferredScrollableViewportSize(table.getPreferredSize());

        JScrollPane scrollPane = new JScrollPane( table );
        add( scrollPane );

        String[] items = { "Bread", "Milk", "Tea", "Coffee" };
        JComboBox<String> editor = new JComboBox<String>( items );

        DefaultCellEditor dce = new DefaultCellEditor( editor );
        table.getColumnModel().getColumn(0).setCellEditor(dce);
    }

    /*
     *  The cost is recalculated whenever the quantity or price is changed
     */
    public void tableChanged(TableModelEvent e)
    {
        if (e.getType() == TableModelEvent.UPDATE)
        {
            int row = e.getFirstRow();
            int column = e.getColumn();

            if (column == 1 || column == 2)
            {
                TableModel model = (TableModel)e.getSource();
                int quantity = ((Integer)model.getValueAt(row, 1)).intValue();
                double price = ((Double)model.getValueAt(row, 2)).doubleValue();
                Double value = new Double(quantity * price);
                model.setValueAt(value, row, 3);
            }
        }
    }

    private static void createAndShowGUI()
    {
        JFrame frame = new JFrame("Table Model Listener");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new TableProcessing());
        frame.pack();
        frame.setLocationByPlatform( true );
        frame.setVisible( true );
    }

    public static void main(String[] args) throws Exception
    {
        EventQueue.invokeLater( () -> createAndShowGUI() );
/*
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowGUI();
            }
        });
*/
    }
}

StackOverflow使用.setValue时出错

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