java - 组合框和按钮在 java 中不能一起工作

Question

我正在为我的计算机科学课做一个日历项目。目前我正在开发一个主菜单，但我似乎遇到了一个我无法摆脱的错误!当我运行程序时，下拉菜单工作正常，但是当我单击按钮时，终端上会显示一堆错误:

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: 
    javax.swing.JButton cannot be cast to javax.swing.JComboBox 

看来是主要的。任何帮助，将不胜感激!您可以在下面看到我的代码。

/*pictures used in this code were edited by Martha Ibarra. Original PNG image sources are listed below
http://imagespng.com/Detail/1093/White-cat-PNG-Transparent-image.html
http://www.freeiconspng.com/img/40367
http://www.susancalman.com/wp-content/uploads/2015/11/corner-cat.png*/


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

public class MainMenu implements ActionListener
{

  private JPanel panel;
  private JFrame frame;
  private JButton addEvent;
  private JButton delEvent;
  private JLabel label;
  private ImageIcon image;
  TextField text = new TextField(20);
  JLabel displayMessage = new JLabel("Select a CATlendar view or you can ADD or DELETE an event!");

  public MainMenu()
  {
    gui();
  }
 ///draws the main menu
  public void gui()
  {
    frame = new JFrame("CATlendar");
    frame.setVisible(true);
    frame.setSize(600,500);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    FlowLayout lay = new FlowLayout();
    panel= new JPanel();
    panel.setBackground(Color.PINK);
    panel.setLayout(lay);

    addEvent = new JButton("ADD EVENT");
    addEvent.setPreferredSize(new Dimension(200, 200));
    addEvent.addActionListener(this);
    ImageIcon catAdd = new ImageIcon(getClass().getResource("im-hungry.png"));
    addEvent.setIcon(catAdd);


    delEvent = new JButton("DELETE EVENT");
    delEvent.setPreferredSize(new Dimension(200, 200));
    delEvent.addActionListener(this);
    ImageIcon catDel = new ImageIcon(getClass().getResource("tres-quatro.png"));
    delEvent.setIcon(catDel);

    image= new ImageIcon(getClass().getResource("uno-dos.png"));
    label=new JLabel(image);

    String[] viewList = { "Weekly", "Daily", "Monthly" };
    JComboBox viewTypes = new JComboBox(viewList);
    viewTypes.setSelectedIndex(0);
    viewTypes.addActionListener(this);


    panel.add(viewTypes);
    panel.add(label);
    panel.add(addEvent);
    panel.add(delEvent);
    frame.add(panel);
    panel.add(displayMessage);
    panel.setVisible(true);
  }
  //corresponding to what the user choses to do this method will change the event hashmap or display a calendar view.
  public void actionPerformed(ActionEvent e)
  {     JComboBox cb = (JComboBox)e.getSource();
        String viewSelect = (String)cb.getSelectedItem();

         if(e.getActionCommand().equals("ADD EVENT"))
         {
           panel.add(text);
           displayMessage.setText("Enter the date of the event you would like to delete ");
           String eventDate = text.getText();
         }else if(e.getActionCommand().equals("DELETE EVENT"))
         {
           panel.add(text);
           displayMessage.setText("Enter the date of the event you would like to add");
           String eventDelDate = text.getText();
         }else if(viewSelect.equals("Weekly"))
         {
           displayMessage.setText("You selected a weekly view");
         }else if(viewSelect.equals("Daily"))
         {
           displayMessage.setText("You selected a daily view");
         }else if(viewSelect.equals("Monthly"))
         {
           displayMessage.setText("You selected a monthly view");
         }else
         {
           displayMessage.setText("pick a view");
         }
  }
  public static void main(String [] args)
  {
    new MainMenu();
  }

}

Answer 1

您的问题:如果事件源是按钮，您尝试访问组合框事件。如果您想在这种情况下访问组合框，您应该提供对此对象的引用。例如:

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

public class MainMenu implements ActionListener
{

    private JPanel panel;
    private JFrame frame;
    private JButton addEvent;
    private JButton delEvent;
    private JLabel label;
    private ImageIcon image;
    private JComboBox viewTypes;
    TextField text = new TextField(20);
    JLabel displayMessage = new JLabel("Select a CATlendar view or you can ADD or DELETE an event!");

    public MainMenu()
    {
        gui();
    }
    ///draws the main menu
    public void gui()
    {

        FlowLayout lay = new FlowLayout();
        panel= new JPanel();
        panel.setBackground(Color.PINK);
        panel.setLayout(lay);

        addEvent = new JButton("ADD EVENT");
        addEvent.setPreferredSize(new Dimension(200, 200));
        addEvent.addActionListener(this);
        ImageIcon catAdd = new ImageIcon(getClass().getResource("im-hungry.png"));
        addEvent.setIcon(catAdd);


        delEvent = new JButton("DELETE EVENT");
        delEvent.setPreferredSize(new Dimension(200, 200));
        delEvent.addActionListener(this);
        ImageIcon catDel = new ImageIcon(getClass().getResource("tres-quatro.png"));
        delEvent.setIcon(catDel);

        image= new ImageIcon(getClass().getResource("uno-dos.png"));
        label=new JLabel("Test");

        String[] viewList = { "Weekly", "Daily", "Monthly" };
        viewTypes = new JComboBox(viewList);
        viewTypes.setSelectedIndex(0);
        viewTypes.addActionListener(this);


        panel.add(viewTypes);
        panel.add(label);
        panel.add(addEvent);
        panel.add(delEvent);
        panel.add(displayMessage);
        panel.setVisible(true);
        frame = new JFrame("CATlendar");
        frame.setVisible(true);
        frame.setSize(600,500);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(panel);
        frame.pack();
    }
    //corresponding to what the user choses to do this method will change the event hashmap or display a calendar view.
    public void actionPerformed(ActionEvent e) {
        String viewSelect = (String)viewTypes.getSelectedItem();

        if(e.getActionCommand().equals("ADD EVENT"))
        {
            panel.add(text);
            displayMessage.setText("Enter the date of the event you would like to delete ");
            String eventDate = text.getText();
        }else if(e.getActionCommand().equals("DELETE EVENT"))
        {
            panel.add(text);    
            displayMessage.setText("Enter the date of the event you would like to add");
            String eventDelDate = text.getText();
        }else if(viewSelect.equals("Weekly"))
        {
            displayMessage.setText("You selected a weekly view");
        }else if(viewSelect.equals("Daily"))
        {
            displayMessage.setText("You selected a daily view");
        }else if(viewSelect.equals("Monthly"))
        {
            displayMessage.setText("You selected a monthly view");
        }else
        {
            displayMessage.setText("pick a view");
        }
        panel.revalidate();
        panel.repaint();
        SwingUtilities.windowForComponent(panel).pack();
    }
    public static void main(String [] args)
    {
        new MainMenu();
    }

}