/**
  *
  * @param value 要四舍五入的值
  * @param scale 小數點后要取的位數
  * @return
  */
 public static double round(double value,int scale){
 BigDecimal bd=new BigDecimal(value);
 BigDecimal divisor=new BigDecimal(1);
 BigDecimal returnValue=bd.divide(divisor, scale,BigDecimal.ROUND_HALF_UP );
 return returnValue.doubleValue();
 }


txt.addFocusListener(new FocusAdapter() {
    public void focusLost(FocusEvent e) {
     if (e.isTemporary()) {
      return;
     }
     checkFullSize(txt, "人名", 20);
    }
   });
public boolean checkFullSize(JTextComponent comp, String desc, int digit) {

  if (checkHarf(comp.getText())) {
   comp.requestFocus();
   JOptionPane.showMessageDialog(null, "full size");
   comp.requestFocus();
   return false;
  }

  if (comp.getText().length() > digit) {
   JOptionPane.showMessageDialog(null, "exceed digit");
   comp.requestFocus();
   return false;
  }

  return true;
 }

 /**
  * 是否為半角
  * @param 字符串
  * @return 半角true 全角false
  */
 private boolean checkHarf(String item) {

  byte[] bytes = item.getBytes();
  int beams = item.length();
  if (beams == bytes.length) {
   return true;
  } else {
   return false;
  }
 }