在双向流动的给水管网管段上，应采用闸阀或（）。

A．止回阀

B．截止阀

C．蝶阀

D．球阀

本题程序的功能是程序的主窗口有一个“登录”按钮和两个文本框——“请输入密码：”和“密码验证…”，用户在密码框中输入密码后单击“登录”按钮，然后与预先定义的密码比较(密码预设定为password)，如果相同，则在“密码验证…，’文本框中提示“通过！”否则提示“失败!”。“密码验证…”文本框是只读的。请将下述程序补充完整(注意：不得改动程序的结构，不得增行或删行)。
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class simple

public static void main(String[] args)

LoginFrame frame = new LoginFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame,show ();


class LoginFrame extends JFrame
public LoginFrame()

setTitle("simple");
setSize(WIDTH,HEIGHT);
Container contentPane = getContentPane();
JPanel textPanel = new JPanel();
JLabel inputPassword = new JLabel("请输入密码:",JLabel.CENTER);
MyPassword = new JPasswordField(20);
textPanel.add(inputPassword);
textPanel.add(myPassword);
JLabel checkedPassword = new JLabel("密码验证...",JLabel.LEFT);
CheckPassword = new JTextField(20);
______;
textPanel.add(checkedPassword);
textPanel.add(checkPassword);
loginButton = new JButton("登录");
loginButton.addActionListener(new LoginAction());
textPane1.add(ioginButton);
contentPane.add(textPanel);

private class LoginAction implements ActionListener

public void actionPerformed(ActionEvent event)

char[] s = myPassword.getPassword();
String gets = new String(s);
if(gets.equals(CHECKPASSWORD))

checkPassword,setText ("通过!");

else

checkPassword.setText ("失败");



public static final int WIDTH = 280;
public static final int HEIGHT = 180;
public static final String CHECKPASSWORD = "password";
______;
private JTextField checkPassword;
private JButton loginButton;