import java.awt.Dimension;import java.awt.Toolkit;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JLabel;import javax.swing.JOptionPane;import javax.swing.JPasswordField;import javax.swing.JTextField;//主類，程序的入口public class begin{ public static void main(String[] args) { new begindemo("這是我的管理系統"); }}class begindemo extends JFrame{ //登錄的用戶名和密碼 private final String userName = "123"; private final String password = "123"; //聲明屏幕的寬高，程序窗口的寬高 private int windowWidth; private int windowHeight; private int screenSizeWidth; private int screenSizeHeight; //構造函數， public begindemo(String title) { super(title); //設置標題 this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //設置能關閉窗口 this.setSize(600, 600); //設置窗口的大小 this.setLayout(null); //設置程序默認布局格式為空，以便于后期自己簡單的設置布局 this.setResizable(false); //設置不可縮放 init();   //執行初始化函數（將用戶名密碼等組件加入到面板中） this.setVisible(true); //使程序可見 } public void init() { //給屏幕的寬度高度，程序窗口的寬度高度賦值 Dimension dimension = Toolkit.getDefaultToolkit().getScreenSize(); screenSizeWidth = (int) dimension.getWidth(); screenSizeHeight = (int) dimension.getHeight(); windowWidth = this.getWidth(); windowHeight = this.getHeight(); //設置程序窗口的位置為屏幕的正中央 this.setLocation(screenSizeWidth / 2 - windowWidth / 2,  screenSizeHeight / 2 - windowHeight / 2); // 聲明姓名，密碼的標簽 JLabel username_label = new JLabel("姓名"); JLabel password_label = new JLabel("密碼"); // 聲明姓名輸入框和密碼輸入框 final JTextField user_field = new JTextField(); final JPasswordField password_field = new JPasswordField(); //聲明登錄按鈕 JButton login_btn = new JButton("登錄"); //設置各個標簽和輸入框的大小和位置 username_label.setBounds(150, 100, 100, 50); password_label.setBounds(150, 200, 100, 50); user_field.setBounds(200, 100, 300, 50); password_field.setBounds(200, 200, 300, 50); login_btn.setBounds(300, 300, 100, 50); this.add(username_label); this.add(password_label); this.add(user_field); this.add(password_field); this.add(login_btn); //登錄按鈕的監聽器 login_btn.addActionListener(new ActionListener() {  @SuppressWarnings("deprecation")  @Override  //當按鈕被單擊時自動調動這個方法  public void actionPerformed(ActionEvent event)  {  //如果用戶名和密碼都是123，那么彈出對話框顯示登錄成功，并且開啟另一個主框架（主頁）  if (user_field.getText().equals(userName)   && password_field.getText().equals(password))  {   JOptionPane.showMessageDialog(null, "登錄成功", "Login",    JOptionPane.INFORMATION_MESSAGE);   //聲明主頁   JFrame home_page = new JFrame("主頁");   //給主頁設置位置   home_page.setLocation(screenSizeWidth / 2 - windowWidth / 2    + 50, screenSizeHeight / 2 - windowHeight / 2 + 50);   //給主頁設置大小   home_page.setSize(windowWidth, windowHeight);   //設置主頁能夠關閉，并且登錄成功后將登錄頁面隱藏   home_page.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);   home_page.setVisible(true);   setVisible(false);//登錄頁面隱藏  } else //反之，登錄不成功，重新登錄  {   JOptionPane.showMessageDialog(null, "登錄失敗，請重新登錄", "Login",    JOptionPane.INFORMATION_MESSAGE);   //設置輸入框的內容為空，讓用戶重新輸入   user_field.setText("");   password_field.setText("");  }  } }); }}

package demo;import java.awt.Dimension;import java.awt.Toolkit;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JLabel;import javax.swing.JOptionPane;import javax.swing.JPasswordField;import javax.swing.JTextField;//主類，程序的入口public class begin{ public static void main(String[] args) { new begindemo("這是我的管理系統"); new student(); }}class begindemo extends JFrame{ //登錄的用戶名和密碼 private final String userName = "123"; private final String password = "123"; //聲明屏幕的寬高，程序窗口的寬高 private int windowWidth; private int windowHeight; private int screenSizeWidth; private int screenSizeHeight; //構造函數， public begindemo(String title) { super(title); //設置標題 this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //設置能關閉窗口 this.setSize(600, 600); //設置窗口的大小 this.setLayout(null); //設置程序默認布局格式為空，以便于后期自己簡單的設置布局 this.setResizable(false); //設置不可縮放 init();   //執行初始化函數（將用戶名密碼等組件加入到面板中） this.setVisible(true); //使程序可見 } public void init() { //給屏幕的寬度高度，程序窗口的寬度高度賦值 Dimension dimension = Toolkit.getDefaultToolkit().getScreenSize(); screenSizeWidth = (int) dimension.getWidth(); screenSizeHeight = (int) dimension.getHeight(); windowWidth = this.getWidth(); windowHeight = this.getHeight(); //設置程序窗口的位置為屏幕的正中央 this.setLocation(screenSizeWidth / 2 - windowWidth / 2,  screenSizeHeight / 2 - windowHeight / 2); // 聲明姓名，密碼的標簽 JLabel username_label = new JLabel("姓名"); JLabel password_label = new JLabel("密碼"); // 聲明姓名輸入框和密碼輸入框 final JTextField user_field = new JTextField(); final JPasswordField password_field = new JPasswordField(); //聲明登錄按鈕 JButton login_btn = new JButton("登錄"); //設置各個標簽和輸入框的大小和位置 username_label.setBounds(150, 100, 100, 50); password_label.setBounds(150, 200, 100, 50); user_field.setBounds(200, 100, 300, 50); password_field.setBounds(200, 200, 300, 50); login_btn.setBounds(300, 300, 100, 50); this.add(username_label); this.add(password_label); this.add(user_field); this.add(password_field); this.add(login_btn); //登錄按鈕的監聽器 login_btn.addActionListener(new ActionListener() {  @SuppressWarnings("deprecation")  @Override  //當按鈕被單擊時自動調動這個方法  public void actionPerformed(ActionEvent event)  {  //如果用戶名和密碼都是123，那么彈出對話框顯示登錄成功，并且開啟另一個主框架（主頁）  if (user_field.getText().equals(userName)   && password_field.getText().equals(password))  {   JOptionPane.showMessageDialog(null, "登錄成功", "Login",    JOptionPane.INFORMATION_MESSAGE);   //聲明主頁   JFrame home_page = new JFrame("主頁");   //給主頁設置位置   home_page.setLocation(screenSizeWidth / 2 - windowWidth / 2    + 50, screenSizeHeight / 2 - windowHeight / 2 + 50);   //給主頁設置大小   home_page.setSize(windowWidth, windowHeight);   //設置主頁能夠關閉，并且登錄成功后將登錄頁面隱藏   home_page.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);   home_page.setVisible(true);   setVisible(false);//登錄頁面隱藏  } else //反之，登錄不成功，重新登錄  {   JOptionPane.showMessageDialog(null, "登錄失敗，請重新登錄", "Login",    JOptionPane.INFORMATION_MESSAGE);   //設置輸入框的內容為空，讓用戶重新輸入   user_field.setText("");   password_field.setText("");  }  } }); }}//聲明一個學生類，方便以后添加學生信息用class student{ private String name; private String sex; private int number; //學號 private String class_; //班級 private double grade; //默認構造函數，new一個對象的時候會自動調用 public student() { this.name = ""; this.number = 0; this.class_ = ""; this.grade = 0; System.out.println("這是一個學生"); } //重載的構造函數 public student(String name, int number, String class_, double grade) { this.name = name; this.number = number; this.class_ = class_; this.grade = grade; } //下面是設置名字性別學號等的函數，以后在輸入學生信息存儲的時候會調用，現在先寫出來方便以后調用 public void setName(String name) { this.name = name; } public void setSex(String sex) { this.sex = sex; } public void setNumber(int number) { this.number = number; } public void setClass(String class_) { this.class_ = class_; } public void setGrade(double grade) { this.grade = grade; } //下面是幾個得到學生姓名性別等的函數，在以后顯示學生信息的時候調用它來顯示學生的信息到窗口上。 public String getName() { return this.name; } public String getSex()  {  return this.sex;  } public int getNumber()  {  return this.number;  } public String getClass_() { return this.class_; } public double getGrade()  {  return this.grade;  } //和上面的函數差不多用來一下設置一個學生的所有個人信息 public void setAll(String name, String sex, int number, String class_,double grade)  {  this.name=name;  this.number=number;  this.sex=sex;  this.class_ = class_;  this.grade = grade; } //一下得到一個學生的所有信息，就不用一個一個getName或者getSex了 public String getAll()  {  String output="";  output+=getName()+" "+getSex()+" "+getNumber()+" "+getClass_()+" "+getGrade();  return output;  } }