Question

我正在尝试将ActionListener添加到我的Java程序中的一个按钮，但是它的方法会导致错误发生。这是我的代码：

import javax.swing.*;//import the packages needed for gui
import java.awt.*;
import java.awt.event.*;
public class Calculator {
    public static void main(String[] args) {
        JFrame window = new JFrame("Window");// makes a JFrame
        window.setSize(300, 350);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel(new FlowLayout());// makes the panel,
                                                    // textfield and buttons
        JTextField textField = new JTextField(20);
        JButton openbracket = new JButton("(");
        JButton closebracket = new JButton(")");
        JButton clearbutton = new JButton("C");
        JButton arcsin = new JButton("arcsin");
        JButton arccos = new JButton("arccos");
        JButton arctan = new JButton("arctan");
        JButton sin = new JButton("sin");
        JButton cos = new JButton("cos");
        JButton tan = new JButton("tan");
        JButton log = new JButton("log");
        JButton seven = new JButton("7");
        JButton eight = new JButton("8");
        JButton nine = new JButton("9");
        JButton four = new JButton("4");
        JButton five = new JButton("5");
        JButton six = new JButton("6");
        JButton one = new JButton("1");
        JButton two = new JButton("2");
        JButton three = new JButton("3");
        JButton zero = new JButton("0");
        JButton radixpoint = new JButton(".");
        JButton equal = new JButton("=");
        String values = null;
        class Listener implements ActionListener {
            public void actionPerformed(ActionEvent e) {
                values = values + "3";
                textField.setText(values);
            }
        }
        panel.add(textField);// adding all the things
        window.add(panel);
        panel.add(openbracket);
        panel.add(closebracket);
        panel.add(clearbutton);
        panel.add(arcsin);
        panel.add(arccos);
        panel.add(arctan);
        panel.add(sin);
        panel.add(cos);
        panel.add(tan);
        panel.add(log);
        panel.add(nine);
        panel.add(eight);
        panel.add(seven);
        panel.add(six);
        panel.add(five);
        panel.add(four);
        panel.add(three);
        panel.add(two);
        panel.add(one);
        panel.add(zero);
        panel.add(radixpoint);
        panel.add(equal);
        window.setVisible(true);
    }
}

我收到的错误消息是：

Calculator.java:36: local variable values is accessed from within inner class; needs to be declared final values = values + "3"; ^

Calculator.java:36: local variable values is accessed from within inner class; needs to be declared final values = values + "3"; ^

Calculator.java:37: local variable values is accessed from within inner class; needs to be declared final textField.setText(values); ^

Calculator.java:37: local variable textField is accessed from within inner class; needs to be declared final textField.setText(values); ^

4 errors

编译器希望我将String对象和JTextField对象声明为final，但如果我将它们声明为final，我将无法更改它们。如何在不更改对象的情况下使计算器正常工作？

Answer 1

好吧，为了使这段代码能够编译，你需要将String值和JTextField textField作为main的静态成员。这是因为那些来自静态主方法。

public class Calculator {

static String values = null;
static JTextField textField = new JTextField(20);
...

如何编译程序？

1 个答案: