Question

我需要帮助解决这个问题。 BlueJ上的错误消息说“无法找到符号 - 变量SevenContinentsFrame。我是初学者，不知道该做什么，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();

您是从Swing API创建JFrame，而不是SevenContients的实例，也是JFrame。

SevenContinents SevenContinentsFrame = new SevenContinents();

这就是......

SevenContinentsFrame.add(button1);

您引用的是不存在的名称。您已在main方法中创建了具有该名称的变量，但它在SevenContinents构造函数中不可见。只需删除名称即可。 E.g。

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

您还需要将()添加到getSource，为动作侦听器中引用的按钮使用正确的变量名称，然后更改按钮显示的布局。

更正后的代码

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);
    }
}

Answer 2

您的班级名称为SevenContinents，您正在尝试访问不存在的SevenContinentsFrame。使用SevenContinentsFrame和中提琴更改对SevenContinents的所有引用！

Answer 3

这是你的完整代码尝试这个它经过测试，如果你使用任何其他IDE而不是BlueJ更改是在这行中做的更好

它不是JFrame，而是你的班级名称

  JFrame SevenContinentsFrame = new JFrame();

这是什么

SevenContinentsFrame.add(button1);

你也没有添加容器，如果你使用数组作为你的按钮会更好容器的代码

Container cp = getContentPane();
        cp.add(pane);

最后我删除了你的工具并将其替换为我将所有按钮添加到面板

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

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

        }

        JButton button1;  
        JButton button2;  
        JButton button3;  
        JButton button4;  
        JButton button5;  
        JButton button6; 
        JButton button7; 

       public SevenContinents()
        {

             //BUTTONS!!!

            setSize(500,500);
            setDefaultCloseOperation(SevenContinents.EXIT_ON_CLOSE);

            button1 = new JButton("1");
            button2 = new JButton("2");
            button3 = new JButton("3");
            button4 = new JButton("4");
            button5 = new JButton("5");
            button6 = new JButton("6");
            button7 = new JButton("7");






            JPanel pane = new JPanel();
            pane.add(button1);
            pane.add(button2);
            pane.add(button3);
            pane.add(button4);
            pane.add(button5);
            pane.add(button6);
            pane.add(button7);

            Container cp = getContentPane();
            cp.add(pane);


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

        }


private class addButtonWatcher implements ActionListener{
        @Override
        public void actionPerformed(ActionEvent a)
        {
            Object buttonPressed= a.getSource();
            if(buttonPressed.equals(button1))
           {

            }
            if(buttonPressed.equals(button2))
            {
                System.out.println("You chose...");
            }
            if(buttonPressed.equals(button3))
            {
                System.out.println("You chose...");
            }
            if(buttonPressed == button4)
            {
                System.out.println("You chose...");
            }
            if(buttonPressed == button5)
            {
                System.out.println("You chose...");
            }
            if(buttonPressed == button6)
            {
                System.out.println("You chose...");
            }
            if(buttonPressed == button7)
            {
                System.out.println("You chose...");
            }

        }
}


   }

按钮ActionListener错误

3 个答案: