java - 按钮 Action 监听器错误

Question

我需要帮助解决这个问题。 BlueJ 上的错误消息显示“找不到符号 - 变量 SevenContinentsFrame。我是一个初学者，不知道该怎么做，并且已经在这个代码上工作了几个小时。

    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import javax.swing.JFrame;
    import javax.swing.JButton;
    public class SevenContinents  extends JFrame implements ActionListener
    {
        JButton button1 = new JButton("1");
        JButton button2 = new JButton("2");
        JButton button3 = new JButton("3");
        JButton button4 = new JButton("4");
        JButton button5 = new JButton("5");
        JButton button6 = new JButton("6");
        JButton button7 = new JButton("7");

       public SevenContinents()
        {

             //BUTTONS!!!

            setSize(1500,1000);

            button1.addActionListener(this);
            button2.addActionListener(this);
            button3.addActionListener(this);
            button4.addActionListener(this);
            button5.addActionListener(this);
            button6.addActionListener(this);
            button7.addActionListener(this);

            SevenContinentsFrame.add(button1);
            SevenContinentsFrame.add(button2);
            SevenContinentsFrame.add(button3);
            SevenContinentsFrame.add(button4);
            SevenContinentsFrame.add(button5);
            SevenContinentsFrame.add(button6);
            SevenContinentsFrame.add(button7);
        }

        public void actionPerformed(ActionEvent e)
        {
            if(e.getSource == btn1)
           {
                System.out.println("You chose...");
            }
            if(e.getSource == btn2)
            {
                System.out.println("You chose...");
            }
            if(e.getSource == btn3)
            {
                System.out.println("You chose...");
            }
            if(e.getSource == btn4)
            {
                System.out.println("You chose...");
            }
            if(e.getSource == btn5)
            {
                System.out.println("You chose...");
            }
            if(e.getSource == btn6)
            {
                System.out.println("You chose...");
            }
            if(e.getSource == btn7)
            {
                System.out.println("You chose...");
            }

        }

        public static void main(String[] args)
        {
            JFrame SevenContinentsFrame = new JFrame();
            SevenContinentsFrame.setVisible(true);
            SevenContinentsFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);
        }

   } 

Answer 1

 JFrame SevenContinentsFrame = new JFrame();

您正在从 Swing API 创建一个 JFrame，而不是 SevenContients 的实例，它也是一个 JFrame。

SevenContinents SevenContinentsFrame = new SevenContinents();

还有这个...

SevenContinentsFrame.add(button1);

您引用的名称不存在。您已在 main 方法中创建了一个具有该名称的变量，但它在 SevenContinents 构造函数中不可见。只需删除名称即可。例如

add(button1);
add(button2);
.
.
.

您还需要将 () 添加到 getSource，为操作监听器中引用的按钮使用正确的变量名称，并更改布局以便按钮显示。

更正的代码

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JButton;

public class SevenContinents extends JFrame implements ActionListener
{
    JButton button1 = new JButton("1");
    JButton button2 = new JButton("2");
    JButton button3 = new JButton("3");
    JButton button4 = new JButton("4");
    JButton button5 = new JButton("5");
    JButton button6 = new JButton("6");
    JButton button7 = new JButton("7");

    public SevenContinents()
    {

        //BUTTONS!!!
        setSize(1500, 1000);

        button1.addActionListener(this);
        button2.addActionListener(this);
        button3.addActionListener(this);
        button4.addActionListener(this);
        button5.addActionListener(this);
        button6.addActionListener(this);
        button7.addActionListener(this);

        setLayout(new FlowLayout());
        add(button1);
        add(button2);
        add(button3);
        add(button4);
        add(button5);
        add(button6);
        add(button7);
    }

    public void actionPerformed(ActionEvent e)
    {
        if (e.getSource() == button1) {
            System.out.println("You chose...");
        }
        if (e.getSource() == button2) {
            System.out.println("You chose...");
        }
        if (e.getSource() == button3) {
            System.out.println("You chose...");
        }
        if (e.getSource() == button4) {
            System.out.println("You chose...");
        }
        if (e.getSource() == button5) {
            System.out.println("You chose...");
        }
        if (e.getSource() == button6) {
            System.out.println("You chose...");
        }
        if (e.getSource() == button7) {
            System.out.println("You chose...");
        }

    }

    public static void main(String[] args)
    {
        SevenContinents SevenContinentsFrame = new SevenContinents();
        SevenContinentsFrame.setVisible(true);
        SevenContinentsFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}