的JTextField只接受字母和空格

Question

我希望用户只输入字母或空格 如果用户输入其他字符，我想给人以JOptionPane的 消息我已经搜查，我想下面的代码

if (!(Pattern.matches("^[a-zA-Z]+$", answerField1.getText()))) 
     JOptionPane.showMessageDialog(null, "Please enter a valid character", "Error", JOptionPane.ERROR_MESSAGE); 

但现在无论我进入它给人的错误

现在我改变了代码

Pattern letterPattern = Pattern.compile("^[a-zA-Z]+$"); 

if (!(letterPattern.matcher(answerField1.getText()).matches())) 
     { 
    JOptionPane.showMessageDialog(null, "Please enter a valid character", "Error", JOptionPane.ERROR_MESSAGE); 
} 

现在它给消息○只有第一次用户输入号码。 我该如何解决这个问题

Answer 1

使用DocumentFilter，这里是我做了一个例子，它只能接受字母字符和空格：

import javax.swing.JFrame; 
import javax.swing.JTextField; 
import javax.swing.SwingUtilities; 
import javax.swing.text.AbstractDocument; 
import javax.swing.text.AttributeSet; 
import javax.swing.text.BadLocationException; 
import javax.swing.text.DocumentFilter; 
import javax.swing.text.DocumentFilter.FilterBypass; 

public class Test { 

    public Test() { 
     initComponents(); 
    } 

    public static void main(String[] args) { 
     SwingUtilities.invokeLater(new Runnable() { 
      @Override 
      public void run() { 
       new Test(); 
      } 
     }); 
    } 

    private void initComponents() { 
     JFrame frame = new JFrame(); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

     JTextField jtf = new JTextField(); 
     //add filter to document 
     ((AbstractDocument) jtf.getDocument()).setDocumentFilter(new MyDocumentFilter()); 

     frame.add(jtf); 

     frame.pack(); 
     frame.setVisible(true); 
    } 
} 

class MyDocumentFilter extends DocumentFilter { 

    @Override 
    public void replace(FilterBypass fb, int i, int i1, String string, AttributeSet as) throws BadLocationException { 
     for (int n = string.length(); n > 0; n--) {//an inserted string may be more than a single character i.e a copy and paste of 'aaa123d', also we iterate from the back as super.XX implementation will put last insterted string first and so on thus 'aa123d' would be 'daa', but because we iterate from the back its 'aad' like we want 
      char c = string.charAt(n - 1);//get a single character of the string 
      System.out.println(c); 
      if (Character.isAlphabetic(c) || c == ' ') {//if its an alphabetic character or white space 
       super.replace(fb, i, i1, String.valueOf(c), as);//allow update to take place for the given character 
      } else {//it was not an alphabetic character or white space 
       System.out.println("Not allowed"); 
      } 
     } 
    } 

    @Override 
    public void remove(FilterBypass fb, int i, int i1) throws BadLocationException { 
     super.remove(fb, i, i1); 
    } 

    @Override 
    public void insertString(FilterBypass fb, int i, String string, AttributeSet as) throws BadLocationException { 
     super.insertString(fb, i, string, as); 

    } 
} 

Answer 2

你在第一行的末尾有分号。所以它不是真的测试正确。

像这样的声明（这是你所拥有的）：

if (condition) ; 

将执行空语句（;）如果条件为真，然后进入下一行。如果条件不成立，它将转到下一行。这两个操作具有相同的结果。

您可能会尝试在所有“if”语句中使用大括号。有时很繁琐，但很难搞砸。

if (!(Pattern.matches("^[a-zA-Z]+$", answerField1.getText()))) { 
    JOptionPane.showMessageDialog(null, "Please enter a valid character", "Error", JOptionPane.ERROR_MESSAGE); 
} 

这就是我要做的。你可以擦掉分号。