当JTextField为空时

当我按下一个按钮将两个JTextField加在一起时，如果文本字段中没有文本，控制台就会发送错误信息。我想知道如果在文本字段中有一些文本，并且只有在运行代码时我才能做出if语句。这是我的代码！当JTextField为空时

public class java { 

public static void main (String []args){ 

    System.setProperty("apple.laf.useScreenMenuBar", "true"); 
    System.setProperty("com.apple.mrj.application.apple.menu.about.name", "Calculator"); 

    int frameSizeX = 500; 
    int frameSizeY = 184; 

    final JPanel p = new JPanel(); 
    p.setPreferredSize(new Dimension(frameSizeX,frameSizeY)); 

    final JFrame f = new JFrame ("Calculator"); 
    f.setSize(frameSizeX,frameSizeY); 
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    //f.setResizable(false); 
    f.getContentPane().add(p); 

    /*JMenuBar bar = new JMenuBar(); 

    JMenu menu = new JMenu("Test"); 

    menu.add(new JMenuItem("Hej")); 

    menu.add(bar);*/ 

    final JLabel cardi = new JLabel ("First number"); 

    final JTextField firstField = new JTextField(); 
    firstField.setPreferredSize(new Dimension(495, 24)); 

    final JLabel perc = new JLabel("Second number"); 

    final JTextField secField = new JTextField(); 
    secField.setPreferredSize(new Dimension(495, 24)); 

    final JLabel answer = new JLabel("---"); 
    final JLabel answer2 = new JLabel(); 
    answer2.setForeground(Color.red); 

    final JButton percButt = new JButton("Percentage"); 
    percButt.setPreferredSize(new Dimension(120, 24)); 
    percButt.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent evt){ 

      p.getRootPane().setDefaultButton(percButt); 

      double A = Double.parseDouble(firstField.getText()); 
      double B = Double.parseDouble(secField.getText()); 
      double C = A/100; 
      double D = C*B; 

      firstField.setText("" + D); 
      secField.setText(""); 

      answer.setText(A + " % " + B + " = "); 
      answer2.setText("" + D); 
      } 
    }); 

    final JButton subButt = new JButton("Subtraction"); 
    subButt.setPreferredSize(new Dimension(120, 24)); 
    subButt.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent evt){ 

      p.getRootPane().setDefaultButton(subButt); 

      double A = Double.parseDouble(firstField.getText()); 
      double B = Double.parseDouble(secField.getText()); 
      double C = A - B; 
      double D = C; 

      firstField.setText("" + D); 
      secField.setText(""); 

      answer.setText(A + " - " + B + " = "); 
      answer2.setText("" + D);  
      } 
    }); 

    final JButton divButt = new JButton("Division"); 
    divButt.setPreferredSize(new Dimension(120, 24)); 
    divButt.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent evt){ 

      p.getRootPane().setDefaultButton(divButt); 

      double A = Double.parseDouble(firstField.getText()); 
      double B = Double.parseDouble(secField.getText()); 
      double C = A/B; 
      double D = C; 

      firstField.setText("" + D); 
      secField.setText(""); 

      answer.setText(A + "/" + B + " = "); 
      answer2.setText("" + D); 
      } 
    }); 

    final JButton addButt = new JButton("Addition"); 
    addButt.setPreferredSize(new Dimension(120, 24)); 
    addButt.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent evt){ 

      p.getRootPane().setDefaultButton(addButt); 

      double A = Double.parseDouble(firstField.getText()); 
      double B = Double.parseDouble(secField.getText()); 
      double C = A + B; 
      double D = C; 

      firstField.setText("" + D); 
      secField.setText(""); 

      answer.setText(A + " + " + B +" = "); 
      answer2.setText("" + D); 
      } 
    }); 

    p.getRootPane().setDefaultButton(addButt); 

    JButton sweButt = new JButton("Swedish"); 
    sweButt.setPreferredSize(new Dimension(245, 24)); 
    sweButt.addActionListener(new ActionListener() { 
     public void actionPerformed(ActionEvent evt){ 

       addButt.setText("Addition"); 
       subButt.setText("Subtraktion"); 
       divButt.setText("Division"); 
       percButt.setText("Procent"); 
       cardi.setText("Första talet"); 
       perc.setText("Andra talet"); 
       f.setTitle("Kalkulator"); 
      } 
    }); 

    JButton engButt = new JButton("English"); 
    engButt.setPreferredSize(new Dimension(245, 24)); 
    engButt.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent evt){ 

       addButt.setText("Addition"); 
       subButt.setText("Subtraction"); 
       divButt.setText("Division"); 
       percButt.setText("Percentege"); 
       cardi.setText("First number"); 
       perc.setText("Second number"); 
       f.setTitle("Calculator"); 
      } 
    }); 

    p.add(sweButt); 
    p.add(engButt); 
    p.add(cardi); 
    p.add(firstField); 
    p.add(perc); 
    p.add(secField); 
    p.add(addButt); 
    p.add(subButt); 
    p.add(divButt); 
    p.add(percButt); 
    p.add(answer); 
    p.add(answer2); 

    //f.setJMenuBar(bar); 
    f.pack(); 
    f.setVisible(true); 

} 
}

来源

2014-01-12 ntoonio

您已使用必要的方法获取文本。 'firstField.getText（）'。现在你只需要把它包装在一个'if'语句中，并确保这个值不是''''或'null'。 – christopher

无关：[不要使用setXXSize，永远]（http://stackoverflow.com/a/7229519/203657） – kleopatra

而不是'final JTextField firstField = new JTextField（）; firstField.setPreferredSize（new Dimension（495,24））;'尝试类似于'final JTextField firstField = new JTextField（25）;'.. –

double A, B; 
    try { 
     A = Double.parseDouble(firstField.getText()); 
     B = Double.parseDouble(secField.getText()); 
    } catch (NumberFormatException e) { 
     JOptionPane.showMessageDialog(f, "Error", "Please enter two numbers", 
      JOptionPane.ERROR_MESSAGE); 
     return; 
    } 
    double C = A/100; 
    double D = C*B;

来源

2014-01-12 14:59:17

*您可能*考虑将您在*底部的计算* try块。否则你冒险做肮脏的数字计算。只是一个想法。 –

此代码检查，如果你的JTextField的是空。如果为空，则会触发一条消息并返回到主框架。

if(jTextField.getText().trim().length()==0 && jTextField1.getText().trim().length()==0){ 
JOptionPane.showMessageDialog(this,"Please enter two numbers"); 
return; 
}

来源

2014-01-12 15:09:09 Aarav

当JTextField为空时

回答

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