Question

我正在尝试编写GUI温度转换器。它有一个JTextField和两个JButton。 TextField接受用户想要转换的温度，用户按下相应的按钮。每当我点击任何一个按钮时，我得到一个“线程异常”AWT-EventQueue-0“java.lang.NumberFormatException：empty String”错误。请帮助！

public class tempcon extends JFrame {
  private JPanel panel;
  private JLabel messageLabel;
  public JTextField tempC; 
  private JButton calcButton, calcButton1;
  private final int WINDOW_WIDTH = 300;
  private final int WINDOW_HEIGHT = 140;

public tempcon() {
  setTitle("Temperature convertion");
  setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  buildPanel();
  add(panel);
  setVisible(true);
}

public double getTempC(){
 return Double.parseDouble(tempC.getText());
}

private void buildPanel() {
    tempC = new JTextField(10);
    messageLabel = new JLabel("Enter tempurture");
    calcButton = new JButton("Convert to Fahrenheit");
    calcButton1 = new JButton("Convert to Celcius");
    calcButton.addActionListener(new CalcButtonListener());
    calcButton1.addActionListener(new CalcButtonListener1());
    panel = new JPanel();
    panel.add(messageLabel);
    panel.add(tempC);
    panel.add(calcButton);
    panel.add(calcButton1);

}

public static void main(String[] args){
 new tempcon().buildPanel();   
}
}

class CalcButtonListener1 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
        double input;
        double temp;
        input = new tempcon().getTempC();
        temp = input * 1.8 + 32;
        JOptionPane.showMessageDialog(null, "That is " + temp + " 
  degrees Celsius.");
    }

}

 class CalcButtonListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        double input;
        double temp;
        input = new tempcon().getTempC();
        temp = (input - 32)*1.8;
        JOptionPane.showMessageDialog(null, "That is " + temp + " 
 degrees Fehrenheit.");
}

public static void main(String[] args) {
tempcon myTempWindowInstance = new tempcon();
}
}

Answer 1

问题是您正在动作侦听器中重新创建一个新帧：new tempcon().getTempC()。

这些新框架中的文本字段显然是空的，您会收到错误消息。

考虑在任何地方引用tempcon的相同实例，只需替换

new tempcon().getTempC();

带

getTempC();

，它将调用外部getTempC()实例的tempcon方法。

导致以下代码中出现“数字格式异常/空字符串”错误的原因是什么？

1 个答案: