在HTML中,文本域的标记是?下列关于网站主页说法错误的是?

Java 判断是否为空
部分代码如下,全部的文本域都填写完成,插入成功,出现问题一,性别我填过了,为啥会跳出性别提示框?只填部分文本域时,点击按钮时,Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException:empty String 异常,
try {
babycode_ = txt_babycode.getText();
address_ = txt_address.getText();
postcode_ = txt_postcode.getText();
mother_ = txt_mother.getText();
father_ = txt_father.getText();
babysex_ = txt_babysex.getText();
babyweight_ = Double.parseDouble(txt_babyweight.getText());
nursecode_ = txt_nursecode.getText();
birthday_ = txt_birthday.getText();
con = DriverManager.getConnection("jdbc:odbc:hello","","");
sql = con.createStatement();
int k = sql.executeUpdate("INSERT INTO message3 VALUES('" + babycode_ + "','"
+ address_ + "','" + postcode_ + "','"
+ mother_ + "','" + father_ + "','"
+ babysex_ + "'," + babyweight_ + ",'"
+ nursecode_ + "','" + birthday_ + "')");
if(mother_==null){
JOptionPane.showMessageDialog(null,"此项为必填","请完成填写",JOptionPane.INFORMATION_MESSAGE);
}
else if(babycode_ .toString().length()!=4&&nursecode_.toString().length()!=4){
JOptionPane.showMessageDialog(null,"必须是四位数","重新填写",JOptionPane.INFORMATION_MESSAGE);
}
else if(postcode_.toString().length()>6&&babycode_.toString().length()>128){
JOptionPane.showMessageDialog(null,"重新填写","超过了所规定的长度",JOptionPane.INFORMATION_MESSAGE);
}
else if(mother_.toString().length()>12&&father_.toString().length()>12){
JOptionPane.showMessageDialog(null,"重新填写","此项为姓名",JOptionPane.INFORMATION_MESSAGE);
}
else if(babysex_!="女"||babysex_!="男"){
JOptionPane.showMessageDialog(null,"请填写男或女","此项为性别",JOptionPane.INFORMATION_MESSAGE);
}
else if(babysex_==null){
JOptionPane.showMessageDialog(null,"此项为必填","请完成填写",JOptionPane.INFORMATION_MESSAGE);
}
else if(nursecode_==null){
JOptionPane.showMessageDialog(null,"此项为必填","请完成填写",JOptionPane.INFORMATION_MESSAGE);