java无法对非静态字段（操作侦听器）进行静态引用

Question

我修正了错误，但我想问另一种方法来修正这个错误。 我试着做一个基本的计算器，现在我正在和听众一起工作。当我试图调用一个按钮时，它说它不能对非静态字段进行静态引用。以下是主要的类代码：

import javax.swing.*;
import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class CalcComb {
    JPanel windowContent;
    JFormattedTextField displayField;
    static JButton button0;
    static JButton button1;
    static JButton button2;
    static JButton button3;
    static JButton button4;
    static JButton button5;
    static JButton button6;
    static JButton button7;
    static JButton button8;
    static JButton button9;
    static JButton buttonPoint;
    static JButton buttonEqual;
    static JButton buttonplus;
    static JButton buttonminus;
    static JButton buttonclear;
    JPanel p1;
    JPanel p2;

public CalcComb() {
    windowContent = new JPanel();
    BorderLayout bl = new BorderLayout();
    windowContent.setLayout(bl);
    displayField = new JFormattedTextField(0);
    displayField.setHorizontalAlignment(SwingConstants.RIGHT);
    windowContent.add("North", displayField);
    button0=new JButton("0");
    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");
    button8=new JButton("8");
    button9=new JButton("9");
    buttonplus=new JButton("+");
    buttonminus=new JButton("-");
    buttonclear=new JButton("C");
    buttonPoint = new JButton(".");
    buttonEqual=new JButton("=");
    p1 = new JPanel();
    p2 = new JPanel();
    GridLayout gl2 = new GridLayout(3, 1);
    GridLayout gl = new GridLayout(3, 3);
    p1.setLayout(gl);
    p2.setLayout(gl2);
    p1.add(button1);
    p1.add(button2);
    p1.add(button3);
    p1.add(button4);
    p1.add(button5);
    p1.add(button6);
    p1.add(button7);
    p1.add(button8);
    p1.add(button9);
    p1.add(button0);
    p1.add(buttonPoint);
    p1.add(buttonEqual);
    p2.add(buttonplus);
    p2.add(buttonminus);
    p2.add(buttonclear);
    windowContent.add("West", p2);
    windowContent.add("Center", p1);
    JFrame frame =  new JFrame("Calculator");
    frame.setSize(400, 400);
    frame.setContentPane(windowContent);
    frame.pack();
    frame.setVisible(true);
    CalcEngine engine = new CalcEngine();
    button0.addActionListener(engine);
    button1.addActionListener(engine);
    button2.addActionListener(engine);
    button3.addActionListener(engine);
    button4.addActionListener(engine);
    button5.addActionListener(engine);
    button6.addActionListener(engine);
    button7.addActionListener(engine);
    button8.addActionListener(engine);
    button9.addActionListener(engine);
    buttonplus.addActionListener(engine);
}
public static void main(String[] args) {
    CalcComb calc = new CalcComb();
}
}

以下是我的侦听器类代码：

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

public class CalcEngine implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        Object src = e.getSource();
        JButton clickedButton = (JButton) e.getSource();
        String clickedButtonLabel = clickedButton.getText();
        if(e.getSource() instanceof JButton) {
            JOptionPane.showConfirmDialog(null, "You pressed " + clickedButtonLabel, "Just a test", JOptionPane.PLAIN_MESSAGE);
            if (clickedButton == CalcComb.buttonplus) {
                JOptionPane.showConfirmDialog(null, "Congratulations", "Just one more test", JOptionPane.PLAIN_MESSAGE);
            }
        }
    }
}

有没有办法在每次按下按钮之前不用一个静态字就解决这个问题

Answer 1

您不应该使用static关键字访问CalcComb类中的按钮。必须对JButtons使用setActionCommand()方法为每个按钮设置唯一的字符串。然后在actionPerformed()中，您可以使用getActionCommand（）获取之前设置的唯一字符串，并确定按下了哪个按钮。无需在CalcComb类中使用静态引用：

ActionListener actionListener = new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        switch (e.getActionCommand()) {
        case "PLUS":
            // DO SOMTHING:
            break;
        case "MULT":
            // DO SOMTHING:
            break;
        default:
            break;
        } 
    }
};

JButton b = new JButton("+");
b.setActionCommand("PLUS");
b.addActionListener(actionListener);

JButton b1 = new JButton("*");
b1.setActionCommand("MULT");
b1.addActionListener(actionListener);

此外，您可能希望避免在init（）方法或构造函数中定义ActionListener实现。一个很好的实践是CalcComb类实现ActionListener intreface，通过这种方式，您在CalcComb类中有actionPerformed方法，但无论如何，使用setActionCommand()和getActionCommand()方法比使用类的成员变量检查引用检查要好：

public class CalcComb implements ActionListener{
...
...


    @Override
    public void actionPerformed(ActionEvent e) {
        switch (e.getActionCommand()) {
        case "PLUS":
            // DO SOMETHING:
            break;
        case "MULT":
            // DO SOMETHING:
            break;
        default:
            break;
        } 
    }
}

祝你好运

Answer 2

您可以使用以下过程：

 if (clickedButton == new CalcComb().buttonplus) {
            JOptionPane.showConfirmDialog(null, "Congratulations", "Just one  more test", JOptionPane.PLAIN_MESSAGE);
        }