Question

对于使用ItemListener和ItemEvent的行，我收到此错误。我把**放在我得到它的地方。

import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JOptionPane;
import javax.swing.JTextField;


public class gui extends JFrame {

private JTextField tf;
private JCheckBox boldbox;
private JCheckBox italicbox;

public gui() {
    super("The title");
    setLayout(new FlowLayout());

    tf = new JTextField("This is a sentence", 20);
    tf.setFont(new Font("Serif", Font.PLAIN, 14));
    add(tf);

    boldbox = new JCheckBox("bold");
    italicbox = new JCheckBox("italic");
    add(boldbox);
    add(italicbox);

    HandlerClass handler = new HandlerClass();
    boldbox.addItemListener(handler);
    italicbox.addItemListener(handler);
}

private class HandlerClass implements *ActionListener* {
    public void itemStateChanged(*ActionEvent* event) {
        Font font = null;

        if (boldbox.isSelected()&& italicbox.isSelected()) 
            font = new Font("Serif", Font.BOLD + Font.ITALIC, 14);
        else if(boldbox.isSelected()) 
                font = new Font("Serif", Font.BOLD, 14);
        else if(italicbox.isSelected())
                    font = new Font("Serif", Font.ITALIC, 14);
        else font = new Font("Serif", Font.PLAIN, 14);

                        tf.setFont(font);
      }
   }            
}

你能帮我理解为什么我会收到这个错误吗？领导该教程的人不会遇到这些错误。

编辑：

import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JOptionPane;
import javax.swing.JTextField;




public class gui extends JFrame {

private JTextField tf;
private JCheckBox boldbox;
private JCheckBox italicbox;

public gui() {
    super("The title");
    setLayout(new FlowLayout());

    tf = new JTextField("This is a sentence", 20);
    tf.setFont(new Font("Serif", Font.PLAIN, 14));
    add(tf);

    boldbox = new JCheckBox("bold");
    italicbox = new JCheckBox("italic");
    add(boldbox);
    add(italicbox);

    HandlerClass handler = new HandlerClass();
    boldbox.addActionListener(handler);
    italicbox.addActionListener(handler);
}

private class HandlerClass implements ActionListener {
    @Override
    public void ActionPerformed(ActionEvent event) {
        Font font = null;

        if (boldbox.isSelected()&& italicbox.isSelected()) 
            font = new Font("Serif", Font.BOLD + Font.ITALIC, 14);
        else if(boldbox.isSelected()) 
                font = new Font("Serif", Font.BOLD, 14);
        else if(italicbox.isSelected())
                    font = new Font("Serif", Font.ITALIC, 14);
        else font = new Font("Serif", Font.PLAIN, 14);

                        tf.setFont(font);
    }
}           
}

Answer 1

您必须导入ItemEvent类。

import java.awt.event.ItemEvent

Answer 2

您应该将ItemListener更改为ActionListener，将ItemEvent更改为ActionEvent。

它应该是这样的：

private class HandlerClass implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent event) {
        Font font = null;
        if (boldbox.isSelected() && italicbox.isSelected()) 
            font = new Font("Serif", Font.BOLD + Font.ITALIC, 14);
        else if(boldbox.isSelected()) 
            font = new Font("Serif", Font.BOLD, 14);
        else if(italicbox.isSelected())
            font = new Font("Serif", Font.ITALIC, 14);
        else font = new Font("Serif", Font.PLAIN, 14);
            tf.setFont(font);
      }
   }            
}

Answer 3

您的代码有2个错误。第一个是您应该导入java.awt.event.ItemListener & ItemEvent而不是ActionListener/ActionEvent。因此，在您的HandlerClass声明中，您应该已实现ItemListener，并且事件对象的类型必须为ItemEvent（在您的itemStateChanged方法中）

import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.event.ItemListener;
import java.awt.event.ItemEvent;
import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JOptionPane;
import javax.swing.JTextField;


public class gui extends JFrame {

private JTextField tf;
private JCheckBox boldbox;
private JCheckBox italicbox;

public gui() {
    super("The title");
    setLayout(new FlowLayout());

    tf = new JTextField("This is a sentence", 20);
    tf.setFont(new Font("Serif", Font.PLAIN, 14));
    add(tf);

    boldbox = new JCheckBox("bold");
    italicbox = new JCheckBox("italic");
    add(boldbox);
    add(italicbox);

    HandlerClass handler = new HandlerClass();
    boldbox.addItemListener(handler);
    italicbox.addItemListener(handler);
}

private class HandlerClass implements ItemListener {
    public void itemStateChanged(ItemEvent event) {
        Font font = null;

        if (boldbox.isSelected()&& italicbox.isSelected()) 
            font = new Font("Serif", Font.BOLD + Font.ITALIC, 14);
        else if(boldbox.isSelected()) 
                font = new Font("Serif", Font.BOLD, 14);
        else if(italicbox.isSelected())
                    font = new Font("Serif", Font.ITALIC, 14);
        else font = new Font("Serif", Font.PLAIN, 14);

                        tf.setFont(font);
      }
   }            
}

这段代码是TheNewBoston在他的第65篇Java编程教程中写的。

无法解决一个类型？

3 个答案: