JTextField：如何限制字符数？

Question

Please have a look at the following code.

import java.awt.FlowLayout;
import java.awt.GridLayout;
import javax.swing.*;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;


public class Bean extends JFrame
{
    private JTextField field1, field2, field3, field4;
    private JLabel text;
    private JButton ok, cancel;
    private JPanel centerPanel,southPanel, textPanel;
    private GridLayout grid;
    private FlowLayout flow1, flow2;

    public Bean()
    {
        //Declaring instance Variables

        field1 = new JTextField(10);

        field2 = new JTextField(5);
        field3 = new JTextField(5);
        field4 = new JTextField(5);        
        text = new JLabel("Insert Your Numbers Here");

      AbstractDocument d = (AbstractDocument) field1.getDocument();
      d.setDocumentFilter(new Bean.Field1Listener());


        ok = new JButton("OK");
        cancel = new JButton("Cancel");


        /***********************Creating the main view*************************/
        centerPanel = new JPanel();
        grid = new GridLayout(2,1,1,1);



        //Adding TextFields
        textPanel = new JPanel();
        flow1 = new FlowLayout(FlowLayout.CENTER);
        textPanel.setLayout(flow1);

        textPanel.add(field1);




        //Adding Buttons
        southPanel = new JPanel();
        southPanel.setLayout(new FlowLayout(FlowLayout.RIGHT));
        southPanel.add(ok);
        southPanel.add(cancel);


        //Creating Center View
        centerPanel.setLayout(grid);
        centerPanel.add(text);
        centerPanel.add(textPanel);


        //Gathering everything together
        getContentPane().add(centerPanel,"Center");
        getContentPane().add(southPanel,"South");


        this.setSize(500,200);
        this.validate();
        this.setVisible(true);
        this.setLocationRelativeTo(null);

        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    }

    private class Field1Listener extends DocumentFilter
    {

       @Override  
        public void insertString(DocumentFilter.FilterBypass fb, int offset, String string, AttributeSet attr) throws BadLocationException  
        {
            if(fb.getDocument().getLength()+string.length()>5)
            {
                return;
            }

            fb.insertString(offset, string, attr);

        }  


        @Override  
        public void remove(DocumentFilter.FilterBypass fb, int offset, int length) throws BadLocationException 
        {  

            fb.insertString(offset, "", null);
        }  



        @Override  
        public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attrs)throws BadLocationException 
        {  



                 if(fb.getDocument().getLength()+text.length()>5)
                 {
                    System.out.println("OK");
                    return;
                }

                fb.insertString(offset, text, attrs);
        }
    }

    public static void main(String[]args)
    {
        new Bean();
    }
}

In here, I am trying to limit the number of character to 5. OK, it stops inserting anymore characters when it reaches 5, but the case is, it also doesn't allow to delete the inserted characters, replace, or anything. How to correct this issue?

Answer 1

simply change your current remove method:

 @Override  
 public void remove(DocumentFilter.FilterBypass fb, int offset, int length) throws BadLocationException 
 {  

     fb.insertString(offset, "", null);
 } 

for this one:

 @Override  
 public void remove(DocumentFilter.FilterBypass fb, int offset, int length) throws BadLocationException 
 {  
     fb.remove(offset, length);
 }

it should now work.

Answer 2

您应该创建自己的类来检查是否提供了比最大允许长度更多的输入：请参阅http://www.java2s.com/Tutorial/Java/0240__Swing/LimitJTextFieldinputtoamaximumlength.htm上的示例。