Java 单选按钮变量错误

Question

所以这现在可以工作了，我修复了变量调用错误。但我得到:

Exception in thread "main" java.lang.NullPointerException
    at Radio.buildPanel(Radio.java:56)
    at Radio.<init>(Radio.java:33)
    at Radio.main(Radio.java:74)

我的 GUI 弹出但是是空白的，现在是什么情况？我现在无法弄清楚问题是什么。

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




public class Radio extends JFrame 
{

    private JPanel Panel;
    private JPanel buttonPanel;
    private JTextField base;
    private JTextField width;
    private JRadioButton squareArea;
    private JRadioButton parallelogramArea;
    private JLabel messageLabel;
    private JTextField text;
    private final int WINDOW_WIDTH = 550;
    private final int WINDOW_HEIGHT = 550;
    private ButtonGroup radioButtonGroup;
    private JRadioButton radioButton1;
    private JRadioButton radioButton2;
    double pTotal;
    double sTotal;

    public Radio()
    {
        setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
        setTitle("Area Calculator");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
        buildPanel();
        add(Panel);

    }

    public void init()
    {
     setLayout(new BorderLayout());
     add(buttonPanel, BorderLayout.SOUTH);
    }
    private void buildPanel() 
    {
        JLabel messageLabel1 = new JLabel("Please enter the base: ");
        JTextField base = new JTextField(10);
        JLabel messageLabel2 = new JLabel("Please enter the width: ");
        JTextField width = new JTextField(10);
        JRadioButton squareArea = new JRadioButton("Choice 1", true);
        JRadioButton parallelogramArea = new JRadioButton("Choice 2");
        ButtonGroup group = new ButtonGroup();
        JButton calcButton = new JButton("Calculate");
        calcButton.setBackground(Color.BLUE);
        calcButton.setForeground(Color.PINK);
        calcButton.addActionListener(new CalcButtonListener());
        Panel.add(messageLabel1);
        Panel.add(base);
        Panel.add(messageLabel2);
        Panel.add(width);
        group.add(squareArea);
        group.add(parallelogramArea);
        buttonPanel.add(squareArea);
        buttonPanel.add(parallelogramArea);
        Panel.add(calcButton);
        Panel.add(buttonPanel);
    }




    public static void main (String[] args)
    {

        Radio radio = new Radio();
    }

    private class CalcButtonListener implements ActionListener
    {
        @Override
        public void actionPerformed(ActionEvent e) 
        {


            if (parallelogramArea.isSelected());
            {
                pTotal = Double.parseDouble(base.getText()) * Double.parseDouble(width.getText());
                JOptionPane.showMessageDialog(null, "The Area is: " + pTotal);
            }


            if (squareArea.isSelected())
            {

                 sTotal = Double.parseDouble(base.getText()) * Double.parseDouble(width.getText());
                 JOptionPane.showMessageDialog(null, "The Area is: " + sTotal);
            }
        }
    }
}

解决这个问题非常重要，在此先感谢您。

Answer 1

第一个错误意味着当您调用 buildPanel(String, String) 时，您需要使用 2 个字符串参数传递给该函数。目前您没有传递参数。第二个错误意味着您尝试使用的变量未定义，因为范围问题意味着当您尝试在方法中使用它们时它们未定义。