如何设置TextField内容长度最大限制

Question

我想让TextField中的内容只能输入数字或英文字母,并设置它的最大长度不可超过某个值,该怎么设啊?
   还一个问题,如何能做到将JTable表格中的内容能按我的要求排序,并由我来设置显示哪行不显示哪行.

Answer 1

我Blog中写过一个这样的例子,希望对你有帮助:
http://blog.csdn.net/mq612/archive/2006/09/29/1305413.aspx

Answer 2

通过Document实现：
myTextField.setDocument ( new PlainDocument ()
        {
            public void insertString( int offset , String s ,
                                      AttributeSet attributeSet ) throws
                BadLocationException
            {
                if ( s == null || offset < 0 )
                {
                    return;
                }                                for ( int i = 0; i < s.length; i++ )
                {
                    if ( getLength () > MAX_LENGTH - 1 or 
      !Character.isLetterOrDigit(s.charAt(i))
                    {                        
                            JOptionPane.showMessageDialog ( null ,
                                "Invalid char!" ,
                                "Error",
                                JOptionPane.YES_OPTION );
                            break;                           
                    }       
           super.insertString ( offset + i , s.substring ( i , i + 1 ) ,
                                         attributeSet );
                }
                return;
            }
        } );

Answer 3

哥哥,我是初学者,你这个我不太会用,看我把它加到这里怎么弄能没错误?import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.text.BadLocationException;
import javax.swing.text.PlainDocument;public class Text extends JFrame {JPanel panel=new JPanel();
JLabel label=new JLabel("用户名");
JTextField textfield=new JTextField();
protected static final int MAX_LENGTH = 8;
/**
 * Launch the application
 * @param args
 */
public static void main(String args[]) {
try {
Text frame = new Text();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
public Text() {
super();
setBounds(100, 100, 500, 375);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
getContentPane().add(panel);
panel.setLayout(new GridBagLayout());
final GridBagConstraints gridBagConstraints = new GridBagConstraints();
gridBagConstraints.gridx = 0;
gridBagConstraints.gridy = 0;
gridBagConstraints.insets = new Insets(10, 100, 100, 0);
panel.add(label, gridBagConstraints);
final GridBagConstraints gridBagConstraints_1 = new GridBagConstraints();
gridBagConstraints_1.ipadx = 120;
gridBagConstraints_1.gridx = 1;
gridBagConstraints_1.gridy = 0;
gridBagConstraints_1.insets = new Insets(5, 20, 100, 218);
panel.add(textfield, gridBagConstraints_1);

textfield.setDocument ( new PlainDocument ()
        {
            public void insertString( int offset , String s ,
                                      AttributeSet attributeSet ) throws
                BadLocationException
            {
                if ( s == null || offset < 0 )
                {
                    return;
                }                                 for ( int i = 0; i < s.length; i++ )
                {
                    if ( getLength () > MAX_LENGTH - 1 or 
      !Character.isLetterOrDigit(s.charAt(i))
                    {                        
                            JOptionPane.showMessageDialog ( null ,
                                "Invalid char!" ,
                                "Error",
                                JOptionPane.YES_OPTION );
                            break;                           
                    }       
          super.insertString ( offset + i , s.substring ( i , i + 1 ) ,
                                         attributeSet );
                }
                return;
            }
        } );
}
}

Answer 4

1. 导入 import javax.swing.text.AttributeSet;
2. 循环和条件语句不对：
for ( int i = 0; i < s.length() ; i++ )
{
   if ( getLength () > MAX_LENGTH - 1 || 
   !Character.isLetterOrDigit(s.charAt(i)))