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单例模式的应用
2022-07-15 23:15:00 【谢三公主】
【实验目的】
- 掌握单例模式（Singleton）的特点
- 分析具体问题，请分别使用四种安全单例模式进行设计。
【实验内容和要求】
例2.6关于一个单位的互联网连接问题的软件设计中，单利模式部分采用的是标准单例模式，现在要求改变其设计，使用线性安全的单例模式。重新设计并且编写代码实现该互联网连接问题。具体要求以及代码实现参见光盘中的实验部分。
【模式代码】
1饿汉式
2 双重检测
代码部分1：
package bbb;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/*==================================================*/
// This is a sigleton class, only one instance of the class can be created.
// To use this class, you cannot use constructor because it has been
// claimed private. You can only use the static method getInstance(),
// which, in case if the instance doesent exist, will create and return an
// instance of LogonGUI to the client class. otherwise, if an instance of
// LogonGUI has already been created before, this method will just
// return that instance to the client class.
/*==================================================*/
public class SingleLogonGUI extends JFrame {
public static final String LOGON = "Log On";
public static final String EXIT = "Exit";
private String USERNM="mikesun";
private String PASSWD = "opensesame";
private JTextField txtUser;
private JTextField txtPassWord;
// private static SingleLogonGUI instance = null;
private volatile static SingleLogonGUI instance = null;
private JTextField txtInstruction;
private SingleLogonGUI() {
super("SingleLogonGUI - Singleton");
initializeGUI();
}
public static SingleLogonGUI getInstance() {
if (instance == null) {
synchronized (SingleLogonGUI.class) {
if (instance == null) {
instance = new SingleLogonGUI();
}
}
}
return instance;
}
public void initializeGUI() {
JLabel lblUsrName = new JLabel("User Name");
JLabel lblPassWord = new JLabel("Password");
txtUser = new JTextField(USERNM);
txtPassWord = new JTextField(PASSWD);
JButton btnLogon = new JButton(LOGON);
btnLogon.setMnemonic(KeyEvent.VK_S);
JButton btnExit = new JButton(EXIT);
btnExit.setMnemonic(KeyEvent.VK_X);
ButtonHandler vf = new ButtonHandler();
btnLogon.addActionListener(vf);
btnExit.addActionListener(vf);
JPanel buttonPanel = new JPanel();
GridBagLayout gridbag = new GridBagLayout();
buttonPanel.setLayout(gridbag);
GridBagConstraints gbc = new GridBagConstraints();
buttonPanel.add(lblUsrName);
buttonPanel.add(txtUser);
buttonPanel.add(lblPassWord);
buttonPanel.add(txtPassWord);
buttonPanel.add(btnLogon);
buttonPanel.add(btnExit);
gbc.insets.top = 5;
gbc.insets.bottom = 5;
gbc.insets.left = 5;
gbc.insets.right = 5;
gbc.gridx = 0;
gbc.gridy = 0;
gridbag.setConstraints(lblUsrName, gbc);
gbc.anchor = GridBagConstraints.WEST;
gbc.gridx = 1;
gbc.gridy = 0;
gridbag.setConstraints(txtUser, gbc);
gbc.gridx = 0;
gbc.gridy = 1;
gridbag.setConstraints(lblPassWord, gbc);
gbc.anchor = GridBagConstraints.WEST;
gbc.gridx = 1;
gbc.gridy = 1;
gridbag.setConstraints(txtPassWord, gbc);
gbc.anchor = GridBagConstraints.EAST;
gbc.insets.left = 2;
gbc.insets.right = 2;
gbc.insets.top = 40;
gbc.gridx = 0;
gbc.gridy = 6;
gridbag.setConstraints(btnLogon, gbc);
gbc.anchor = GridBagConstraints.WEST;
gbc.gridx = 1;
gbc.gridy = 6;
gridbag.setConstraints(btnExit, gbc);
Container contentPane = getContentPane();
contentPane.add(buttonPanel, BorderLayout.CENTER);
txtInstruction = new JTextField();
txtInstruction.setBackground(Color.pink);
contentPane.add( txtInstruction, BorderLayout.NORTH);
setSize(320, 200);
setVisible(true);
}
public boolean isValideCustomer() {
String usr = txtUser.getText();
String pwd = txtPassWord.getText();
if(usr.equals(USERNM) && pwd.equals(PASSWD))
return true;
else
return false;
}
private void issueWarning(){
txtInstruction.setText("Invalide user name or password.");
}
private void issueSuccess(){
txtInstruction.setText("You have been successfully connected to the web.");
}
class ButtonHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals(EXIT)) {
System.exit(1);
}
if (e.getActionCommand().equals(LOGON)) {
boolean isValideCus = isValideCustomer();
if(isValideCus == false){
//logon failed
issueWarning();
}
else{
//logon successfully
issueSuccess();
}
}
}
}
}// end of class
代码部分2：
package bbb;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ClientUI extends JFrame{
private static final String CONNECT = "Create Connection";
private static final String EXIT = "Exit";
private JTextField txtInstruction;
private SingleLogonGUI objLogon = null;
public ClientUI() {
super("ClientUI - Singleton Pattern");
JButton btnConnect = new JButton(CONNECT);
JButton btnExit = new JButton(EXIT);
btnConnect.setMnemonic(KeyEvent.VK_S);
btnExit.setMnemonic(KeyEvent.VK_X);
ButtonHandler vf = new ButtonHandler();
btnConnect.addActionListener(vf);
btnExit.addActionListener(vf);
JPanel buttonPanel = new JPanel();
buttonPanel.setBackground(Color.green);
buttonPanel.add(btnConnect);
buttonPanel.add(btnExit);
txtInstruction = new JTextField("Click to get a connection");
txtInstruction.setBackground(Color.green);
Container contentPane = getContentPane();
contentPane.setLayout(new BorderLayout());
contentPane.add(buttonPanel, "South");
contentPane.add(txtInstruction, "Center");
setSize(320, 120);
setVisible(true);
}
private void issueWarning(){
txtInstruction.setText("Error. You cannot start a second connection.");
}
class ButtonHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals(EXIT)) {
System.exit(1);
}
else if (e.getActionCommand().equals(CONNECT)) {
if(objLogon == null)
objLogon = SingleLogonGUI.getInstance();
else
issueWarning();
}
}
}
public static void main(String[] args) {
ClientUI connection = new ClientUI();
}
}// end of class
3 静态内部类
代码1
package bbb;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/*==================================================*/
// This is a sigleton class, only one instance of the class can be created.
// To use this class, you cannot use constructor because it has been
// claimed private. You can only use the static method getInstance(),
// which, in case if the instance doesent exist, will create and return an
// instance of LogonGUI to the client class. otherwise, if an instance of
// LogonGUI has already been created before, this method will just
// return that instance to the client class.
/*==================================================*/
public class SingleLogonGUI extends JFrame {
public static final String LOGON = "Log On";
public static final String EXIT = "Exit";
private String USERNM="mikesun";
private String PASSWD = "opensesame";
private JTextField txtUser;
private JTextField txtPassWord;
// private static SingleLogonGUI instance = null;
private volatile static SingleLogonGUI instance = null;
private JTextField txtInstruction;
//静态内部类
private static class SingletonHolder {
//静态初始化器机制初始化本数据（保证了同步控制，线程安全）
private static SingleLogonGUI instance = new SingleLogonGUI();
}
private SingleLogonGUI() {
super("SingleLogonGUI - Singleton");
initializeGUI();
}
public static SingleLogonGUI getInstance() {
return SingletonHolder.instance;
}
public void initializeGUI() {
JLabel lblUsrName = new JLabel("User Name");
JLabel lblPassWord = new JLabel("Password");
txtUser = new JTextField(USERNM);
txtPassWord = new JTextField(PASSWD);
JButton btnLogon = new JButton(LOGON);
btnLogon.setMnemonic(KeyEvent.VK_S);
JButton btnExit = new JButton(EXIT);
btnExit.setMnemonic(KeyEvent.VK_X);
ButtonHandler vf = new ButtonHandler();
btnLogon.addActionListener(vf);
btnExit.addActionListener(vf);
JPanel buttonPanel = new JPanel();
GridBagLayout gridbag = new GridBagLayout();
buttonPanel.setLayout(gridbag);
GridBagConstraints gbc = new GridBagConstraints();
buttonPanel.add(lblUsrName);
buttonPanel.add(txtUser);
buttonPanel.add(lblPassWord);
buttonPanel.add(txtPassWord);
buttonPanel.add(btnLogon);
buttonPanel.add(btnExit);
gbc.insets.top = 5;
gbc.insets.bottom = 5;
gbc.insets.left = 5;
gbc.insets.right = 5;
gbc.gridx = 0;
gbc.gridy = 0;
gridbag.setConstraints(lblUsrName, gbc);
gbc.anchor = GridBagConstraints.WEST;
gbc.gridx = 1;
gbc.gridy = 0;
gridbag.setConstraints(txtUser, gbc);
gbc.gridx = 0;
gbc.gridy = 1;
gridbag.setConstraints(lblPassWord, gbc);
gbc.anchor = GridBagConstraints.WEST;
gbc.gridx = 1;
gbc.gridy = 1;
gridbag.setConstraints(txtPassWord, gbc);
gbc.anchor = GridBagConstraints.EAST;
gbc.insets.left = 2;
gbc.insets.right = 2;
gbc.insets.top = 40;
gbc.gridx = 0;
gbc.gridy = 6;
gridbag.setConstraints(btnLogon, gbc);
gbc.anchor = GridBagConstraints.WEST;
gbc.gridx = 1;
gbc.gridy = 6;
gridbag.setConstraints(btnExit, gbc);
Container contentPane = getContentPane();
contentPane.add(buttonPanel, BorderLayout.CENTER);
txtInstruction = new JTextField();
txtInstruction.setBackground(Color.pink);
contentPane.add( txtInstruction, BorderLayout.NORTH);
setSize(320, 200);
setVisible(true);
}
public boolean isValideCustomer() {
String usr = txtUser.getText();
String pwd = txtPassWord.getText();
if(usr.equals(USERNM) && pwd.equals(PASSWD))
return true;
else
return false;
}
private void issueWarning(){
txtInstruction.setText("Invalide user name or password.");
}
private void issueSuccess(){
txtInstruction.setText("You have been successfully connected to the web.");
}
class ButtonHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals(EXIT)) {
System.exit(1);
}
if (e.getActionCommand().equals(LOGON)) {
boolean isValideCus = isValideCustomer();
if(isValideCus == false){
//logon failed
issueWarning();
}
else{
//logon successfully
issueSuccess();
}
}
}
}
}// end of class
代码2
package bbb;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ClientUI extends JFrame{
private static final String CONNECT = "Create Connection";
private static final String EXIT = "Exit";
private JTextField txtInstruction;
private SingleLogonGUI objLogon = null;
public ClientUI() {
super("ClientUI - Singleton Pattern");
JButton btnConnect = new JButton(CONNECT);
JButton btnExit = new JButton(EXIT);
btnConnect.setMnemonic(KeyEvent.VK_S);
btnExit.setMnemonic(KeyEvent.VK_X);
ButtonHandler vf = new ButtonHandler();
btnConnect.addActionListener(vf);
btnExit.addActionListener(vf);
JPanel buttonPanel = new JPanel();
buttonPanel.setBackground(Color.green);
buttonPanel.add(btnConnect);
buttonPanel.add(btnExit);
txtInstruction = new JTextField("Click to get a connection");
txtInstruction.setBackground(Color.green);
Container contentPane = getContentPane();
contentPane.setLayout(new BorderLayout());
contentPane.add(buttonPanel, "South");
contentPane.add(txtInstruction, "Center");
setSize(320, 120);
setVisible(true);
}
private void issueWarning(){
txtInstruction.setText("Error. You cannot start a second connection.");
}
class ButtonHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals(EXIT)) {
System.exit(1);
}
else if (e.getActionCommand().equals(CONNECT)) {
if(objLogon == null)
objLogon = SingleLogonGUI.getInstance();
else
issueWarning();
}
}
}
public static void main(String[] args) {
ClientUI connection = new ClientUI();
}
}// end of class
4 枚举类
代码1：
package bbb;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/*==================================================*/
// This is a sigleton class, only one instance of the class can be created.
// To use this class, you cannot use constructor because it has been
// claimed private. You can only use the static method getInstance(),
// which, in case if the instance doesent exist, will create and return an
// instance of LogonGUI to the client class. otherwise, if an instance of
// LogonGUI has already been created before, this method will just
// return that instance to the client class.
/*==================================================*/
public class SingleLogonGUI extends JFrame {
public static final String LOGON = "Log On";
public static final String EXIT = "Exit";
private String USERNM="mikesun";
private String PASSWD = "opensesame";
private JTextField txtUser;
private JTextField txtPassWord;
// private static SingleLogonGUI instance = null;
private volatile static SingleLogonGUI instance = null;
private JTextField txtInstruction;
//
private SingleLogonGUI() {
super("SingleLogonGUI - Singleton");
initializeGUI();
}
/** * 枚举类型是线程安全的，并且只会装载一次 */
private enum Singleton{
INSTANCE;
private final SingleLogonGUI instance;
Singleton(){
instance = new SingleLogonGUI();
}
private SingleLogonGUI getInstance(){
return instance;
}
}
public static SingleLogonGUI getInstance() {
return Singleton.INSTANCE.getInstance();
}
//
public void initializeGUI() {
JLabel lblUsrName = new JLabel("User Name");
JLabel lblPassWord = new JLabel("Password");
txtUser = new JTextField(USERNM);
txtPassWord = new JTextField(PASSWD);
JButton btnLogon = new JButton(LOGON);
btnLogon.setMnemonic(KeyEvent.VK_S);
JButton btnExit = new JButton(EXIT);
btnExit.setMnemonic(KeyEvent.VK_X);
ButtonHandler vf = new ButtonHandler();
btnLogon.addActionListener(vf);
btnExit.addActionListener(vf);
JPanel buttonPanel = new JPanel();
GridBagLayout gridbag = new GridBagLayout();
buttonPanel.setLayout(gridbag);
GridBagConstraints gbc = new GridBagConstraints();
buttonPanel.add(lblUsrName);
buttonPanel.add(txtUser);
buttonPanel.add(lblPassWord);
buttonPanel.add(txtPassWord);
buttonPanel.add(btnLogon);
buttonPanel.add(btnExit);
gbc.insets.top = 5;
gbc.insets.bottom = 5;
gbc.insets.left = 5;
gbc.insets.right = 5;
gbc.gridx = 0;
gbc.gridy = 0;
gridbag.setConstraints(lblUsrName, gbc);
gbc.anchor = GridBagConstraints.WEST;
gbc.gridx = 1;
gbc.gridy = 0;
gridbag.setConstraints(txtUser, gbc);
gbc.gridx = 0;
gbc.gridy = 1;
gridbag.setConstraints(lblPassWord, gbc);
gbc.anchor = GridBagConstraints.WEST;
gbc.gridx = 1;
gbc.gridy = 1;
gridbag.setConstraints(txtPassWord, gbc);
gbc.anchor = GridBagConstraints.EAST;
gbc.insets.left = 2;
gbc.insets.right = 2;
gbc.insets.top = 40;
gbc.gridx = 0;
gbc.gridy = 6;
gridbag.setConstraints(btnLogon, gbc);
gbc.anchor = GridBagConstraints.WEST;
gbc.gridx = 1;
gbc.gridy = 6;
gridbag.setConstraints(btnExit, gbc);
Container contentPane = getContentPane();
contentPane.add(buttonPanel, BorderLayout.CENTER);
txtInstruction = new JTextField();
txtInstruction.setBackground(Color.pink);
contentPane.add( txtInstruction, BorderLayout.NORTH);
setSize(320, 200);
setVisible(true);
}
public boolean isValideCustomer() {
String usr = txtUser.getText();
String pwd = txtPassWord.getText();
if(usr.equals(USERNM) && pwd.equals(PASSWD))
return true;
else
return false;
}
private void issueWarning(){
txtInstruction.setText("Invalide user name or password.");
}
private void issueSuccess(){
txtInstruction.setText("You have been successfully connected to the web.");
}
class ButtonHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals(EXIT)) {
System.exit(1);
}
if (e.getActionCommand().equals(LOGON)) {
boolean isValideCus = isValideCustomer();
if(isValideCus == false){
//logon failed
issueWarning();
}
else{
//logon successfully
issueSuccess();
}
}
}
}
}// end of class
代码2
package bbb;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ClientUI extends JFrame{
private static final String CONNECT = "Create Connection";
private static final String EXIT = "Exit";
private JTextField txtInstruction;
private SingleLogonGUI objLogon = null;
public ClientUI() {
super("ClientUI - Singleton Pattern");
JButton btnConnect = new JButton(CONNECT);
JButton btnExit = new JButton(EXIT);
btnConnect.setMnemonic(KeyEvent.VK_S);
btnExit.setMnemonic(KeyEvent.VK_X);
ButtonHandler vf = new ButtonHandler();
btnConnect.addActionListener(vf);
btnExit.addActionListener(vf);
JPanel buttonPanel = new JPanel();
buttonPanel.setBackground(Color.green);
buttonPanel.add(btnConnect);
buttonPanel.add(btnExit);
txtInstruction = new JTextField("Click to get a connection");
txtInstruction.setBackground(Color.green);
Container contentPane = getContentPane();
contentPane.setLayout(new BorderLayout());
contentPane.add(buttonPanel, "South");
contentPane.add(txtInstruction, "Center");
setSize(320, 120);
setVisible(true);
}
private void issueWarning(){
txtInstruction.setText("Error. You cannot start a second connection.");
}
class ButtonHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals(EXIT)) {
System.exit(1);
}
else if (e.getActionCommand().equals(CONNECT)) {
if(objLogon == null)
objLogon = SingleLogonGUI.getInstance();
else
issueWarning();
}
}
}
public static void main(String[] args) {
ClientUI connection = new ClientUI();
}
}// end of class
【运行截图】
1饿汉式
2 双重检测
3 静态内部类
4 枚举类
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