Question

JAVA简单登陆界面代码修改

为何当用户名为空时弹不出窗口 请输入用户名或密码
怎么修改
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class window extends JDialog implements ActionListener//创建监听器
{
JPanel p1=new JPanel();
JPanel p2=new JPanel();
JPanel p3=new JPanel();
JPanel p4=new JPanel();
JPanel p5=new JPanel();
JTextField UserName=new JTextField(15);//定义用户名
JPasswordField Password=new JPasswordField(15);
JButton ok=new JButton("确定");//确定按钮
JButton cancel=new JButton("取消");//取消按钮
public window()//窗口
{
setModal(true);
setBackground(Color.white);
Container contentPane=this.getContentPane();
contentPane.setLayout(new GridLayout(5,1));
p2.add(new JLabel("用户名："));
p2.add(UserName);
p3.add(new JLabel("密 码："));
p3.add(Password);
p4.add(ok);
p4.add(cancel);
ok.addActionListener(this);
cancel.addActionListener(this);
UserName.addActionListener(this);
Password.addActionListener(this);
contentPane.add(p1);
contentPane.add(p2);
contentPane.add(p3);
contentPane.add(p4);
contentPane.add(p5);
this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
setSize(300,200);
Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();
setLocation((screen.width-300)/2,(screen.width-800)/2);
setTitle("欢迎登陆井字游戏");
setResizable(false);
setVisible(true);

}

/**
* @param args
*/
public static void main(String[] args) {
new window();

}

public void actionPerformed(ActionEvent e) {//鼠标监听器
if(e.getSource()==ok||e.getSource()==Password)
{
if(UserName.getText().trim().equals("1")&&String.valueOf(Password.getPassword()).trim().equals("1"))
{
this.dispose();
new game();
}
else if(UserName.getText().trim().equals(null))
{
JOptionPane.showMessageDialog(null,"请输入用户名或密码");
UserName.requestFocus();
}
else
{
JOptionPane.showMessageDialog(null,"用户名或密码错误,请重新输入");
UserName.requestFocus();//鼠标指向Username
UserName.setSelectionStart(0);//选中输入字符从0开始
//UserName.setSelectionEnd(UserName.getText().length());
}
}
else if(e.getSource()==cancel)
{
this.dispose();
System.exit(0);
}
else if(e.getSource()==UserName)
{
Password.requestFocus();//鼠标指向密码
}

}

}

Answer 1

你好，你如果是要输入为空则弹出窗口提示，可用js脚本就OK了
<script LANGUAGE="javascript">
<!--
function check()
{
if(document.F.N.value.length==0){ //F为下面表单提交的form的name，N为用户名称的name
alert("姓名不能为空，请重新输入!");
document.F.N.focus(); //此F,N与以上同理！都是提交表单和用户名的name
return false;
}
}
//-->
</script>

Answer 2

if(name.trim().length()!=0){
//弹出窗口
}else{
//提示用户名为空
}