java - 我需要帮助弄清楚为什么我的清除按钮代码不起作用

Question

我正在为我的 Java 类开发一个项目，但无法让我的清除按钮工作。更具体地说，我在实现 Action 和 ItemListeners 时遇到问题。我的理解是，我需要为我的清除按钮使用 ActionListener，但我需要为我的 ComboBox 使用 ItemListener。我对 Java 很陌生，这是一门入门类(class)。我什至还没有开始编写提交按钮和组合框的代码，我有点不知所措。现在，我可以使用帮助来弄清楚为什么我的清除功能不起作用。任何帮助是极大的赞赏。提前致谢。

这是我在建议后更新的代码:

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

public class cousinsTree extends JApplet

{
Container Panel;
JButton submitButton;
JButton clearButton;
JTextField firstName;
JTextField lastName;
JTextField Address;
JTextField City;
JMenuBar menuBar;
JTextField Total;
JComboBox Service;
JComboBox howOften;
JComboBox numTrees;
LayoutManager setLayout;
String[] TreeList;
String[] numList;
String[] oftenList;


@Override
public void init()
{
    Panel = getContentPane();
    this.setLayout(new FlowLayout());
    TreeList= new String[3];
    TreeList [0] = "Trim";
    TreeList [1] = "Chemical Spray";
    TreeList [2] = "Injection";
    numList = new String[3];
    numList [0] = "0-5";
    numList [1] = "6-10";
    numList [2] = "11 >";
    oftenList = new String[3];
    oftenList [0] = "Monthly";
    oftenList [1] = "Quarterly";
    oftenList [2] = "Annually";     
    Panel.setBackground (Color.green);
    submitButton = new JButton("Submit");
    submitButton.setPreferredSize(new Dimension(100,30));
    clearButton.addActionListener(new clrButton());
    clearButton = new JButton("Clear");
    clearButton.setPreferredSize(new Dimension(100,30));
    firstName = new JTextField("", 10);
    JLabel lblFirstName = new JLabel("First Name");
    lastName = new JTextField("", 10);
    JLabel lblLastName = new JLabel("Last Name");
    Address = new JTextField("", 15);
    JLabel lblAddress = new JLabel("Address");
    City = new JTextField("Columbus", 10);
    JLabel lblCity = new JLabel("City");
    Total = new JTextField("", 10);
    JLabel lblTotal = new JLabel("Total");

    //Service = new TextField("Service (Trim, Chemical Spray, or Injection).", 20);
    JLabel lblService = new JLabel("Service");
    Service=new JComboBox(TreeList);

    JLabel lblhowOften = new JLabel("How often?");
    howOften = new JComboBox(oftenList);

    JLabel lblnumTrees = new JLabel("Number of Trees");
    numTrees = new JComboBox(numList);

/* Configuration */
    //add items to panel
    Panel.add(lblFirstName);
    Panel.add(firstName);
Panel.add(lblLastName);
    Panel.add(lastName);
    Panel.add(lblAddress);
    Panel.add(Address);
    Panel.add(lblCity);
    Panel.add(City);
    Panel.add(lblnumTrees);
    Panel.add(numTrees);
    Panel.add(lblService);
    Panel.add(Service);
    Panel.add(lblhowOften);
    Panel.add(howOften);
    Panel.add(submitButton);
    Panel.add(clearButton);
    Panel.add(lblTotal);
    Panel.add(Total);

    this.setSize(new Dimension(375, 275));
    this.setLocation(0,0);

Service.setSelectedIndex (1);
howOften.setSelectedIndex (1);
numTrees.setSelectedIndex (1);

        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);

        JMenu menuFile = new JMenu("File", true);
            menuFile.setMnemonic(KeyEvent.VK_F);
            menuFile.setDisplayedMnemonicIndex(0);
            menuBar.add(menuFile);

        JMenu menuSave = new JMenu("Save", true);
            menuSave.setMnemonic(KeyEvent.VK_S);
            menuSave.setDisplayedMnemonicIndex(0);
            menuBar.add(menuSave);

        JMenu menuExit = new JMenu("Exit", true);
            menuExit.setMnemonic(KeyEvent.VK_X);
            menuExit.setDisplayedMnemonicIndex(0);
            menuBar.add(menuExit);
}
class clrButton implements ActionListener {
public void actionPerformed(ActionEvent e) {
   // clearButton.addActionListener(this);

     firstName.setText("");
     lastName.setText("");
     Address.setText("");
     City.setText("");           
}
}
class subButton implements ItemListener { 
public void itemStateChanged(ItemEvent e) {
submitButton.addItemListener(this);
Service.addItemListener(this);
numTrees.addItemListener(this);
howOften.addItemListener(this);
}
}
}

我能够让它工作...谢谢大家的帮助。我删除了该类并且它起作用了。这是工作代码:

[代码]

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

public class cousinsTree extends JApplet implements ActionListener
{
Container Panel;
JButton submitButton;
JButton clearButton;
JTextField firstName;
JTextField lastName;
JTextField Address;
JTextField City;
JMenuBar menuBar;
JTextField Total;
JComboBox Service;
JComboBox howOften;
JComboBox numTrees;
LayoutManager setLayout;
String[] TreeList;
String[] numList;
String[] oftenList;

public void init()
{
    Panel = getContentPane();
    this.setLayout(new FlowLayout());
    TreeList= new String[3];
    TreeList [0] = "Trim";
    TreeList [1] = "Chemical Spray";
    TreeList [2] = "Injection";
    numList = new String[3];
    numList [0] = "0-5";
    numList [1] = "6-10";
    numList [2] = "11 >";
    oftenList = new String[3];
    oftenList [0] = "Monthly";
    oftenList [1] = "Quarterly";
    oftenList [2] = "Annually";     
    Panel.setBackground (Color.green);
    submitButton = new JButton("Submit");
    submitButton.setPreferredSize(new Dimension(100,30));
    clearButton = new JButton("Clear");
    clearButton.addActionListener(this);
    clearButton.setPreferredSize(new Dimension(100,30));
    firstName = new JTextField("", 10);
    JLabel lblFirstName = new JLabel("First Name");
    lastName = new JTextField("", 10);
    JLabel lblLastName = new JLabel("Last Name");
    Address = new JTextField("", 15);
    JLabel lblAddress = new JLabel("Address");
    City = new JTextField("Columbus", 10);
    JLabel lblCity = new JLabel("City");
    Total = new JTextField("", 10);
    JLabel lblTotal = new JLabel("Total");

    //Service = new TextField("Service (Trim, Chemical Spray, or Injection).", 20);
    JLabel lblService = new JLabel("Service");
    Service=new JComboBox(TreeList);

    JLabel lblhowOften = new JLabel("How often?");
    howOften = new JComboBox(oftenList);

    JLabel lblnumTrees = new JLabel("Number of Trees");
    numTrees = new JComboBox(numList);

/* Configuration */
    //add items to panel
    Panel.add(lblFirstName);
    Panel.add(firstName);
Panel.add(lblLastName);
    Panel.add(lastName);
    Panel.add(lblAddress);
    Panel.add(Address);
    Panel.add(lblCity);
    Panel.add(City);
    Panel.add(lblnumTrees);
    Panel.add(numTrees);
    Panel.add(lblService);
    Panel.add(Service);
    Panel.add(lblhowOften);
    Panel.add(howOften);
    Panel.add(submitButton);
    Panel.add(clearButton);
    Panel.add(lblTotal);
    Panel.add(Total);



    this.setSize(new Dimension(375, 275));
    this.setLocation(0,0);

Service.setSelectedIndex (1);
howOften.setSelectedIndex (1);
numTrees.setSelectedIndex (1);

        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);

        JMenu menuFile = new JMenu("File", true);
            menuFile.setMnemonic(KeyEvent.VK_F);
            menuFile.setDisplayedMnemonicIndex(0);
            menuBar.add(menuFile);

        JMenu menuSave = new JMenu("Save", true);
            menuSave.setMnemonic(KeyEvent.VK_S);
            menuSave.setDisplayedMnemonicIndex(0);
            menuBar.add(menuSave);

        JMenu menuExit = new JMenu("Exit", true);
            menuExit.setMnemonic(KeyEvent.VK_X);
            menuExit.setDisplayedMnemonicIndex(0);
            menuBar.add(menuExit);


}
public void actionPerformed(ActionEvent e) {
    if(e.getSource() == clearButton) {

     firstName.setText("");
     lastName.setText("");
     Address.setText("");
     City.setText("");           
}
}

} 

[/代码]

Answer 1

添加以下行

  clearButton.addActionListener(new clrButton());

<小时/>

class clrButton implements ActionListener {
  public void actionPerformed(ActionEvent e) {
  //  clearButton.addActionListener(this); Comment it

  // if(e.getSource() == clearButton){-> this line don't need.

     firstName.setText("");
     lastName.setText("");
     Address.setText("");
     City.setText("");            
 }
}