JAVA中TextField的length的控制 （不用监听器）

Question

It is easy
你继承javax.swing.text.PlainDocument再做一个Documnet实现
重写insertString(..)方法,其中进行你的判断,最后不要忘记写super.insertString(..)

Answer 1

TextField它的实现是用C语言的，估计你不大可能控制！

Answer 2

下面的类可以实现你想要设TextField是输入整数还是输入小数，并可设定输入长度，
TextField bm = new TextField();
bm.setDocument(new CustomTextFormator(max_length));
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
import javax.swing.event.*;    
public class CustomTextFormator extends PlainDocument
  {    private String strAllowChar =null;
       private int intMaxLength =0;
       private int intDataType=0;
       private int intPricesion=0;
       public static final int INTEGER_TEXT=1;
       public static final int FLOAT_TEXT=2;
       public static final int DATE_YEAR=3;
       public static final int DATE_MONTH=4;
       //--- Construct Function
       public CustomTextFormator(int intMaxLength)
       {   super();
           this.intMaxLength = intMaxLength;
       }
      //----
       public CustomTextFormator(int intMaxLength, String strCharList)
       {  super();
          this.intMaxLength = intMaxLength;
          this.strAllowChar  = strCharList;
       }
      //----
       public CustomTextFormator(int intMaxLength, int intDataType)
       {  super();
          this.intMaxLength = intMaxLength;
          this.intDataType  = intDataType;
          if(intDataType == this.INTEGER_TEXT)
             this.strAllowChar = "-1234567890";
          else if(intDataType == this.DATE_YEAR)
             this.strAllowChar = "1234567890";
          else if(intDataType == this.DATE_MONTH)
             this.strAllowChar = "1234567890";
          else if(intDataType == this.FLOAT_TEXT)
             this.strAllowChar = "-1234567890.";
       }
      //----
       public CustomTextFormator(int intMaxLength, int intDataType, int intPricesion)
       {  super();
          this.intMaxLength = intMaxLength;
          this.intDataType  = intDataType;
          if(intDataType == this.INTEGER_TEXT)
             this.strAllowChar = "-1234567890";
          else if(intDataType == this.FLOAT_TEXT)
             this.strAllowChar = "-1234567890.";
          this.intPricesion = intPricesion;
       }
      //==== Check Function Panel ===
      public void insertString(int offset, String s, AttributeSet attributeSet) throws BadLocationException
      
      {   
       if (!(s == null)) {
      //-- Check Length
          String strLastText = super.getText(0,super.getLength());
          if(this.intMaxLength>0)
          {  /*if(s.length()>1)
             {  if(s.getBytes().length+strLastText.getBytes().length>=(this.intMaxLength+this.intPricesion+1))
                   s=s.substring(0,this.intMaxLength-strLastText.getBytes().length);
             }
             else*/ 
             {  int intIntegerPos = strLastText.indexOf(".");
                if(intIntegerPos >=0)
                {  if(intIntegerPos>this.intMaxLength)
                      return; 
                   if(strLastText.getBytes().length>=(this.intMaxLength+this.intPricesion+1))
                      return;   
                }
                else
                {  if(strLastText.getBytes().length>=this.intMaxLength && (!s.equals(".")))
                      return;
                }   
                
              }
          }
          //-- Check Char String--
          if(this.strAllowChar instanceof String)
          {   String strCheckChar=null;
              for(int i=0;i<s.length();i++)
              {   strCheckChar=s.substring(i,i+1);
                  if(this.strAllowChar.indexOf(strCheckChar)<0)
                   return;
              }
          }
          //---- Check Signed Position
          int intSignedPos = s.trim().indexOf("-");
          if(intSignedPos >0 && offset>0)
             return;
          //----
          if(this.intDataType == this.DATE_MONTH)
          {  if(strLastText.length()>0)
             {  if(strLastText.compareTo("1")>0)
                   return;
                else if(strLastText.compareTo("1")==0 && s.compareTo("2")>0)
                   return;
                else if(strLastText.compareTo("0")==0 && s.compareTo("0")==0)
                   return;
             }
          }
          //--- Check Precision -
          else if(this.intPricesion >0)
          {  int intDotPos=strLastText.lastIndexOf(".");
             if(s.indexOf(".")>=0)
             {  if(intDotPos >0)
                  return;  //--- 已有点号
                else    //--- 插入点号
                { int intCurrentDotPos = s.indexOf(".");
                  if((s.length()-intCurrentDotPos-1) + (strLastText.length()-offset) > this.intPricesion)
                    return;
                }             }
             if(intDotPos>=0 && (strLastText.trim().length()-intDotPos>this.intPricesion)
                && offset>intDotPos)
               return;
          }
          }
          super.insertString(offset,s,attributeSet);
      }
      //============================
  }