文本框输入内容怎么限制??

Question

如果一个文本框里要求只能输入数字,要怎么做呀?类似于QQ的登录界面的那个输入QQ号那里一样,只要输入非数字就不能输入.这个在java里要怎么实现呀?

Answer 1

import   java.awt.*;   
  import   java.awt.event.*;   
  import   java.text.*;   
  import   javax.swing.*;   
  import   javax.swing.text.*;   
    
  public   class   TestInputNumber   {   
        public   static   void   main(String[]   args)   {       
              FormatTestFrame   frame   =   new   FormatTestFrame();   
              frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);   
              frame.show();   
        }   
  }   
    
  class   FormatTestFrame   extends   JFrame   {       
        public   FormatTestFrame()   {       
              setTitle("FormatTest");   
              setSize(300,   100);   
    
              Container   contentPane   =   getContentPane();   
              JLabel   lblIntField   =   new   JLabel("NumberFilter:");   
              JFormattedTextField   intField   
                    =   new   JFormattedTextField(new     
                          InternationalFormatter(   
                                NumberFormat.getIntegerInstance())   {   
                                protected   DocumentFilter   getDocumentFilter()   {   
                                      return   filter;   
                                }   
                                private   DocumentFilter   filter   =   new   IntFilter();   
                          });   
              intField.setValue(new   Integer(100));   
              intField.setColumns(10);   
    
              JPanel   mainPanel   =   new   JPanel();   
              mainPanel.add(lblIntField);   
              mainPanel.add(intField);   
              contentPane.add(mainPanel,   BorderLayout.CENTER);   
        }   
    
    
          class   IntFilter   extends   DocumentFilter   {   
                public   void   insertString(FilterBypass   fb,   int   offset,     
                      String   string,   AttributeSet   attr)     
                      throws   BadLocationException   {   
                      StringBuffer   buffer   =   new   StringBuffer(string);   
                      for   (int   i   =   buffer.length()   -   1;   i   >=   0;   i--)   {   
                            char   ch   =   buffer.charAt(i);   
                            if   (!Character.isDigit(ch)   &&   ch   !=   '\\'   &&   ch!=KeyEvent.VK_BACK_SPACE   &&   ch!=KeyEvent.VK_ENTER)     
                                  buffer.deleteCharAt(i);   
                      }   
                      super.insertString(fb,   offset,   buffer.toString(),   attr);   
                }   
    
                public   void   replace(FilterBypass   fb,   int   offset,     
                      int   length,   String   string,   AttributeSet   attr)     
                      throws   BadLocationException   {   
                      if   (string   !=   null)   {   
                            StringBuffer   buffer   =   new   StringBuffer(string);   
                            for   (int   i   =   buffer.length()   -   1;   i   >=   0;   i--)   {   
                                  char   ch   =   buffer.charAt(i);   
                                  if   (!Character.isDigit(ch)   &&   ch   !=   '\\'   &&   ch!=KeyEvent.VK_BACK_SPACE   &&   ch!=KeyEvent.VK_ENTER)   
                                        buffer.deleteCharAt(i);   
                            }   
                            string   =   buffer.toString();   
                      }   
                      super.replace(fb,   offset,   length,   string,   attr);   
                }   
          }   
  }   

Answer 2

2）javax.Swing.JTextFieldJTextField和TextField不一样， 他有一个setDocument(Document doc)方法， 可以来设置输入。如import java.awt.*;
import javax.swing.text.*;public void setInputLimited(int min , int max,JtextField text){   text.setDocument(new NumberOnlyDocument());}
public class NumberOnlyDocument
        extends PlainDocument {
    private boolean haveDot = false;
    private int length = 0;
    private double max = Double.MIN_VALUE, min = Double.MAX_VALUE;
   
    public NumberOnlyDocument(double max, double min) {
        if (max >= min) {
            this.max = max;
            this.min = min;
        }
        
    }   
       public void insertString(int offs, String str, AttributeSet a) throws
            BadLocationException {        if (str == null) {
            return;
        }
        char[] number = str.toCharArray();
        for (int i = 0; i < number.length; i++) {
            if (offs == 0) {
                if (! (number[i] >= '0' && number[i] <= '9' || number[i] == '.' ||
                        number[i] == '-' || number[i] == '+')) {
                    if (offs == length - 1) {
                        remove(offs + i, 1);
                    }
                    else {
                        return;
                    }                }
                else {
                    length++;
                }
            }
            else {
                if (!haveDot) {
                    if (! (number[i] >= '0' && number[i] <= '9' || number[i] == '.')) {
                        if (offs == length - 1) {
                            remove(offs + i, 1);
                        }
                        else {
                            return;
                        }
                    }
                    else {
                        if (number[i] == '.') {
                            haveDot = true;
                        }
                        length++;
                    }
                }
                else {
                    if (! (number[i] >= '0' && number[i] <= '9')) {
                        if (offs == length - 1) {
                            remove(offs + i, 1);
                        }
                        else {
                            Toolkit.getDefaultToolkit().beep();
                            return;
                        }
                    }
                    else {
                        length++;
                    }
                }
            }
        }
       
        super.insertString(offs, new String(number), a);
    }
}