☕ Java Programming

import java.awt.*; import java.awt.event.*; // Step 1: Implement ActionListener public class ButtonDemo extends Frame implements ActionListener { Button btn; Label lbl; int clickCount = 0; public ButtonDemo() { btn = new Button("Click Me!"); lbl = new Label("No clicks yet"); // Step 2: Register listener (this class IS the listener) btn.addActionListener(this); setLayout(new FlowLayout()); add(lbl); add(btn); setTitle("Event Demo"); setSize(300, 120); setVisible(true); addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { dispose(); } }); } // Step 3: Override handler method public void actionPerformed(ActionEvent e) { clickCount++; lbl.setText("Clicked " + clickCount + " time(s) | Cmd: " + e.getActionCommand()); } public static void main(String[] args) { new ButtonDemo(); } } // Output: Window opens. On each click label updates with count and command name.

import java.awt.*; import java.awt.event.*; public class MouseDemo extends Frame implements MouseListener { Label lbl = new Label("Move/click mouse here", Label.CENTER); public MouseDemo() { lbl.addMouseListener(this); // Register add(lbl); setSize(350, 150); setVisible(true); addWindowListener(new WindowAdapter(){ public void windowClosing(WindowEvent e){dispose();} }); } public void mouseClicked(MouseEvent e) { lbl.setText("Clicked at ("+e.getX()+","+e.getY()+")"); } public void mousePressed(MouseEvent e) { lbl.setText("Mouse Pressed!"); } public void mouseReleased(MouseEvent e) { lbl.setText("Mouse Released!"); } public void mouseEntered(MouseEvent e) { lbl.setBackground(Color.CYAN); } public void mouseExited(MouseEvent e) { lbl.setBackground(null); } public static void main(String[] a) { new MouseDemo(); } } // Output: Hover → background turns cyan. Click → shows coordinates.

import java.awt.*; import java.awt.event.*; public class KeyDemo extends Frame implements KeyListener { TextField tf = new TextField(20); Label lbl = new Label("Type something..."); public KeyDemo() { tf.addKeyListener(this); setLayout(new FlowLayout()); add(lbl); add(tf); setSize(350, 100); setVisible(true); } public void keyPressed(KeyEvent e) { lbl.setText("Pressed: " + KeyEvent.getKeyText(e.getKeyCode())); } public void keyReleased(KeyEvent e) { lbl.setText("Released: " + e.getKeyChar()); } public void keyTyped(KeyEvent e) { /* called for printable chars */ } public static void main(String[] a) { new KeyDemo(); } } // Output: Press 'A' → "Pressed: A" → "Released: a"

import java.awt.*; import java.awt.event.*; public class AdapterDemo extends Frame { Label lbl = new Label("Use mouse and keyboard"); public AdapterDemo() { setLayout(new FlowLayout()); add(lbl); // Using MouseAdapter — only override mouseClicked (rest are empty) addMouseListener(new MouseAdapter() { public void mouseClicked(MouseEvent e) { lbl.setText("Clicked at: " + e.getX() + "," + e.getY()); } }); // Using KeyAdapter — only override keyPressed addKeyListener(new KeyAdapter() { public void keyPressed(KeyEvent e) { lbl.setText("Key: " + KeyEvent.getKeyText(e.getKeyCode())); } }); // Using WindowAdapter — only override windowClosing addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { dispose(); } }); setTitle("Adapter Demo"); setSize(300, 120); setVisible(true); } public static void main(String[] a) { new AdapterDemo(); } } // Clean! No need to implement all 5/7/3 methods, just the ones we need.

import java.applet.*; import java.awt.*; /* HTML to run: <applet code="LifeCycleDemo.class" width="400" height="220"> <param name="student" value="Ankush"> </applet> */ public class LifeCycleDemo extends Applet { String studentName; int visitCount = 0; int paintCount = 0; // 1. init() — called ONCE at first load public void init() { studentName = getParameter("student"); // Read HTML param if (studentName == null) studentName = "Guest"; setBackground(Color.WHITE); System.out.println("1. init() — Name: " + studentName); } // 2. start() — called after init() and on each page revisit public void start() { visitCount++; System.out.println("2. start() — Visit #" + visitCount); repaint(); // trigger paint() } // 3. paint() — called to draw on applet public void paint(Graphics g) { paintCount++; g.setFont(new Font("Arial", Font.BOLD, 16)); g.setColor(Color.BLUE); g.drawString("Hello, " + studentName + "!", 30, 40); g.setColor(Color.BLACK); g.drawString("Visit count: " + visitCount, 30, 70); g.drawString("Paint count: " + paintCount, 30, 95); // Draw shapes g.setColor(Color.RED); g.fillOval(30, 120, 60, 60); g.setColor(Color.GREEN); g.fillRect(120, 120, 80, 60); g.setColor(Color.ORANGE); g.drawRoundRect(230, 115, 100, 70, 15, 15); g.setColor(Color.GRAY); g.drawString("3. paint() called #" + paintCount, 30, 200); } // 4. stop() — called when user leaves page public void stop() { System.out.println("4. stop() called"); } // 5. destroy() — called when applet removed public void destroy() { System.out.println("5. destroy() — Bye!"); } } /* Console Output: 1. init() — Name: Ankush 2. start() — Visit #1 [user leaves page] 4. stop() called [user returns] 2. start() — Visit #2 [browser closes] 4. stop() called → 5. destroy() — Bye! */

import java.awt.*; import java.awt.event.*; public class AllComponentsDemo extends Frame implements ActionListener { // Declare all components Label lblName, lblCity, lblResult; TextField tfName; TextArea taAddress; Checkbox cbJava, cbPython; CheckboxGroup genderGroup; Checkbox rbMale, rbFemale; Choice cityChoice; List skillList; Scrollbar slider; Button btnSubmit; public AllComponentsDemo() { setLayout(null); // Manual (absolute) positioning // 1. LABEL — displays non-editable text lblName = new Label("Name:"); lblName.setBounds(20, 30, 80, 25); add(lblName); // 2. TEXTFIELD — single-line text input tfName = new TextField("Enter name", 20); tfName.setBounds(110, 30, 200, 25); add(tfName); // 3. TEXTAREA — multi-line text input lblCity = new Label("Address:"); lblCity.setBounds(20, 70, 80, 25); taAddress = new TextArea("City, State", 4, 25); // 4 rows, 25 cols taAddress.setBounds(110, 70, 200, 70); add(lblCity); add(taAddress); // 4. CHECKBOX — toggle (can select multiple) cbJava = new Checkbox("Java", true); // pre-checked cbPython = new Checkbox("Python", false); cbJava.setBounds(20, 155, 100, 25); cbPython.setBounds(130, 155, 100, 25); add(cbJava); add(cbPython); // 5. RADIO BUTTONS — CheckboxGroup makes them mutually exclusive genderGroup = new CheckboxGroup(); rbMale = new Checkbox("Male", genderGroup, true); rbFemale = new Checkbox("Female", genderGroup, false); rbMale.setBounds(20, 190, 80, 25); rbFemale.setBounds(110, 190, 90, 25); add(rbMale); add(rbFemale); // 6. CHOICE — dropdown (select ONE item) cityChoice = new Choice(); cityChoice.add("Delhi"); cityChoice.add("Mumbai"); cityChoice.add("Ludhiana"); cityChoice.add("Bangalore"); cityChoice.select("Ludhiana"); // default selection cityChoice.setBounds(20, 225, 180, 25); add(cityChoice); // 7. LIST — visible list (can allow multi-select) skillList = new List(3, true); // 3 rows, multi-select = true skillList.add("HTML"); skillList.add("CSS"); skillList.add("Java"); skillList.add("SQL"); skillList.setBounds(210, 225, 100, 65); add(skillList); // 8. SCROLLBAR — sliding value control slider = new Scrollbar(Scrollbar.HORIZONTAL, 50, 10, 0, 110); // (orientation, initialValue, visibleAmount, min, max) slider.setBounds(20, 300, 290, 20); add(slider); // 9. BUTTON — clickable btnSubmit = new Button("Submit"); btnSubmit.addActionListener(this); btnSubmit.setBounds(110, 335, 100, 30); add(btnSubmit); // 10. RESULT LABEL lblResult = new Label(""); lblResult.setBounds(20, 375, 310, 25); add(lblResult); setTitle("All AWT Components"); setSize(360, 420); setVisible(true); addWindowListener(new WindowAdapter(){ public void windowClosing(WindowEvent e){dispose();} }); } public void actionPerformed(ActionEvent e) { String name = tfName.getText(); String gender = genderGroup.getSelectedCheckbox().getLabel(); String city = cityChoice.getSelectedItem(); String java = cbJava.getState() ? "Java" : ""; lblResult.setText(name + " | " + gender + " | " + city + " | " + java); } public static void main(String[] a) { new AllComponentsDemo(); } } // Output: Fill form → click Submit → result label shows: "Ankush | Male | Ludhiana | Java"

import java.awt.*; import java.awt.event.*; class DrawCanvas extends Canvas { public void paint(Graphics g) { // Draw various shapes g.setColor(Color.RED); g.fillRect(20, 20, 100, 60); g.setColor(Color.BLUE); g.fillOval(140, 20, 80, 80); g.setColor(Color.GREEN); g.drawRoundRect(240, 20, 90, 60, 20, 20); g.setColor(Color.ORANGE); g.fillArc(20, 110, 100, 80, 0, 270); g.setColor(Color.BLACK); g.drawLine(0, 200, 350, 200); g.setFont(new Font("Arial", Font.BOLD, 14)); g.setColor(Color.MAGENTA); g.drawString("Java AWT Canvas Drawing", 30, 230); } } public class CanvasDemo extends Frame { public CanvasDemo() { DrawCanvas c = new DrawCanvas(); c.setSize(360, 250); c.setBackground(Color.WHITE); add(c); setTitle("Canvas Demo"); setSize(380, 280); setVisible(true); } public static void main(String[] a) { new CanvasDemo(); } }

setLayout(new FlowLayout()); // CENTER alignment, gap=5 setLayout(new FlowLayout(FlowLayout.LEFT)); // Left aligned setLayout(new FlowLayout(FlowLayout.RIGHT, 10, 8)); // Right, hgap=10, vgap=8 // Usage: add(new Button("Home")); add(new Button("About")); add(new Button("Contact")); // Components are added left to right automatically

setLayout(new GridLayout(3, 3, 5, 5)); // 3 rows, 3 cols, gaps=5 String[] keys = {"7","8","9","4","5","6","1","2","3","0",".","+/-"}; for (String k : keys) { add(new Button(k)); // Added left-to-right, top-to-bottom }

// BorderLayout is DEFAULT for Frame — no need to set it // But can set explicitly: setLayout(new BorderLayout(5, 5)); // hgap=5, vgap=5 add(new Button("NORTH"), BorderLayout.NORTH); add(new Button("SOUTH"), BorderLayout.SOUTH); add(new Button("EAST"), BorderLayout.EAST); add(new Button("WEST"), BorderLayout.WEST); add(new TextArea("CENTER — This expands!"), BorderLayout.CENTER);

import java.awt.*; import java.awt.event.*; public class CardLayoutDemo extends Frame implements ActionListener { CardLayout cl = new CardLayout(); Panel cardPanel = new Panel(); Button prev, next; public CardLayoutDemo() { cardPanel.setLayout(cl); // Create pages Panel home = new Panel(); home.add(new Label("🏠 Home Page")); home.setBackground(Color.PINK); Panel about = new Panel(); about.add(new Label("ℹ️ About Page")); about.setBackground(Color.CYAN); Panel contact = new Panel(); contact.add(new Label("📧 Contact")); contact.setBackground(Color.YELLOW); // Add to CardLayout with names cardPanel.add(home, "home"); cardPanel.add(about, "about"); cardPanel.add(contact, "contact"); prev = new Button("◀ Prev"); next = new Button("Next ▶"); prev.addActionListener(this); next.addActionListener(this); Panel nav = new Panel(); nav.add(prev); nav.add(next); Button goHome = new Button("Go Home"); goHome.addActionListener(e -> cl.show(cardPanel, "home")); nav.add(goHome); add(cardPanel, BorderLayout.CENTER); add(nav, BorderLayout.SOUTH); setTitle("CardLayout"); setSize(350, 200); setVisible(true); } public void actionPerformed(ActionEvent e) { if (e.getSource() == next) cl.next(cardPanel); else cl.previous(cardPanel); } public static void main(String[] a) { new CardLayoutDemo(); } }

import java.io.*; import javax.servlet.*; import javax.servlet.http.*; // A complete Servlet example — Student Login public class LoginServlet extends HttpServlet { public void init() throws ServletException { System.out.println("LoginServlet initialized!"); } // Handles GET request: http://localhost:8080/app/login?user=Raj&pass=1234 public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { String user = req.getParameter("user"); String pass = req.getParameter("pass"); processLogin(user, pass, res); } // Handles POST request (form submission — data hidden from URL) public void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { String user = req.getParameter("user"); String pass = req.getParameter("pass"); processLogin(user, pass, res); } private void processLogin(String user, String pass, HttpServletResponse res) throws IOException { res.setContentType("text/html"); PrintWriter out = res.getWriter(); out.println("<html><head><title>Login Result</title></head><body>"); if ("admin".equals(user) && "1234".equals(pass)) { out.println("<h2 style='color:green'>✓ Login Successful!</h2>"); out.println("<p>Welcome, " + user + "!</p>"); } else { out.println("<h2 style='color:red'>✗ Login Failed!</h2>"); out.println("<p>Invalid username or password.</p>"); } out.println("<a href='index.html'>← Back to Login</a>"); out.println("</body></html>"); } public void destroy() { System.out.println("LoginServlet destroyed!"); } } // URL: http://localhost:8080/myapp/login?user=admin&pass=1234 // Output: Login Successful! Welcome, admin!

-- Create database and table (run in MySQL/MariaDB first) CREATE DATABASE college; USE college; CREATE TABLE students ( id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(50) NOT NULL, marks INT DEFAULT 0, city VARCHAR(30), email VARCHAR(80) ); INSERT INTO students (name, marks, city, email) VALUES ('Raj', 85, 'Delhi', 'raj@email.com'), ('Priya', 92, 'Mumbai', 'priya@email.com'), ('Amit', 78, 'Bangalore', 'amit@email.com'), ('Neha', 65, 'Ludhiana', 'neha@email.com'); SELECT * FROM students;

import java.sql.*; public class JDBCConnection { public static void main(String[] args) { String url = "jdbc:mysql://localhost:3306/college"; Connection con = null; Statement stmt = null; ResultSet rs = null; try { // Step 1: Load driver Class.forName("com.mysql.cj.jdbc.Driver"); System.out.println("Step 1: Driver loaded!"); // Step 2: Connect con = DriverManager.getConnection(url, "root", "password"); System.out.println("Step 2: Connected to 'college' database!"); // Step 3: Create Statement stmt = con.createStatement(); System.out.println("Step 3: Statement created!"); // Step 4: Execute query rs = stmt.executeQuery("SELECT * FROM students ORDER BY marks DESC"); System.out.println("Step 4: Query executed!\n"); // Step 5: Process ResultSet System.out.printf("%-4s %-12s %-6s %-12s%n", "ID", "Name", "Marks", "City"); System.out.println("-".repeat(38)); while (rs.next()) { System.out.printf("%-4d %-12s %-6d %-12s%n", rs.getInt("id"), rs.getString("name"), rs.getInt("marks"), rs.getString("city")); } } catch (ClassNotFoundException e) { System.out.println("ERROR: Driver not found! " + e.getMessage()); } catch (SQLException e) { System.out.println("SQL ERROR: " + e.getMessage()); System.out.println("Error Code: " + e.getErrorCode()); } finally { // Step 6: Always close in finally block! try { if (rs != null) rs.close(); if (stmt != null) stmt.close(); if (con != null) con.close(); System.out.println("\nStep 6: All resources closed!"); } catch (SQLException e) { e.printStackTrace(); } } } } /* Output: Step 1: Driver loaded! Step 2: Connected to 'college' database! Step 3: Statement created! Step 4: Query executed! ID Name Marks City -------------------------------------- 2 Priya 92 Mumbai 1 Raj 85 Delhi 3 Amit 78 Bangalore 4 Neha 65 Ludhiana Step 6: All resources closed! */

import java.sql.*; import java.util.Scanner; public class InsertDemo { public static void main(String[] args) throws Exception { Scanner sc = new Scanner(System.in); System.out.print("Enter name: "); String name = sc.nextLine(); System.out.print("Enter marks: "); int marks = sc.nextInt(); sc.nextLine(); System.out.print("Enter city: "); String city = sc.nextLine(); Class.forName("com.mysql.cj.jdbc.Driver"); Connection con = DriverManager.getConnection( "jdbc:mysql://localhost:3306/college", "root", "password"); // Method 1: Statement (AVOID for user input — SQL Injection risk!) // String sql = "INSERT INTO students(name,marks,city) VALUES('" + name + "'," + marks + ",'" + city + "')"; // Method 2: PreparedStatement (ALWAYS use for user input) PreparedStatement ps = con.prepareStatement( "INSERT INTO students(name, marks, city) VALUES(?, ?, ?)"); ps.setString(1, name); // Position 1 = first ? ps.setInt(2, marks); // Position 2 = second ? ps.setString(3, city); // Position 3 = third ? int rows = ps.executeUpdate(); // Execute INSERT System.out.println(rows > 0 ? "✓ Inserted successfully!" : "✗ Insert failed!"); ps.close(); con.close(); } } /* Input: name=Ravi, marks=88, city=Chennai Output: ✓ Inserted successfully! */

import java.sql.*; public class SelectDemo { public static void main(String[] args) throws Exception { Class.forName("com.mysql.cj.jdbc.Driver"); Connection con = DriverManager.getConnection( "jdbc:mysql://localhost:3306/college", "root", "password"); Statement stmt = con.createStatement(); // 1. Get ALL records ResultSet rs = stmt.executeQuery("SELECT * FROM students"); System.out.println("--- All Students ---"); while (rs.next()) { System.out.println(rs.getInt("id") + " | " + rs.getString("name") + " | " + rs.getInt("marks") + " | " + rs.getString("city")); } // 2. Filtered SELECT with PreparedStatement (safe!) PreparedStatement ps = con.prepareStatement( "SELECT name, marks FROM students WHERE marks > ? ORDER BY marks DESC"); ps.setInt(1, 80); ResultSet rs2 = ps.executeQuery(); System.out.println("\n--- Students scoring > 80 ---"); while (rs2.next()) { System.out.println(rs2.getString("name") + " → " + rs2.getInt("marks")); } // 3. Aggregate functions ResultSet rs3 = stmt.executeQuery( "SELECT COUNT(*) AS total, AVG(marks) AS avg, MAX(marks) AS top FROM students"); if (rs3.next()) { System.out.printf("%nTotal: %d | Avg: %.1f | Top: %d%n", rs3.getInt("total"), rs3.getDouble("avg"), rs3.getInt("top")); } rs.close(); rs2.close(); rs3.close(); stmt.close(); ps.close(); con.close(); } } /* Output: --- All Students --- 1 | Raj | 85 | Delhi 2 | Priya | 92 | Mumbai 3 | Amit | 78 | Bangalore 4 | Neha | 65 | Ludhiana --- Students scoring > 80 --- Priya → 92 Raj → 85 Total: 4 | Avg: 80.0 | Top: 92 */

import java.sql.*; public class UpdateDemo { public static void main(String[] args) throws Exception { Class.forName("com.mysql.cj.jdbc.Driver"); Connection con = DriverManager.getConnection( "jdbc:mysql://localhost:3306/college", "root", "password"); // Update marks for a specific student PreparedStatement ps = con.prepareStatement( "UPDATE students SET marks = ? WHERE id = ?"); ps.setInt(1, 95); // new marks ps.setInt(2, 2); // student id int rows = ps.executeUpdate(); System.out.println("Updated: " + rows + " row(s)"); // Verify ResultSet rs = con.createStatement().executeQuery( "SELECT name, marks FROM students WHERE id=2"); if (rs.next()) System.out.println("Now: " + rs.getString("name") + " → " + rs.getInt("marks")); ps.close(); con.close(); } } /* ⚠️ WITHOUT WHERE: UPDATE students SET marks=100; → ALL rows updated! Always include WHERE clause! Output: Updated: 1 row(s) Now: Priya → 95 */

import java.sql.*; public class DeleteDemo { public static void main(String[] args) throws Exception { Class.forName("com.mysql.cj.jdbc.Driver"); Connection con = DriverManager.getConnection( "jdbc:mysql://localhost:3306/college", "root", "password"); // Delete a specific student PreparedStatement ps = con.prepareStatement( "DELETE FROM students WHERE id = ?"); ps.setInt(1, 4); // Delete student with id=4 int rows = ps.executeUpdate(); if (rows > 0) System.out.println("✓ Deleted " + rows + " student(s)!"); else System.out.println("✗ No student found with that ID"); // Delete by condition — remove students with marks < 40 PreparedStatement ps2 = con.prepareStatement( "DELETE FROM students WHERE marks < ?"); ps2.setInt(1, 40); System.out.println("Failed students removed: " + ps2.executeUpdate()); ps.close(); ps2.close(); con.close(); } } /* ⚠️ WITHOUT WHERE: DELETE FROM students; → ALL rows deleted! Output: ✓ Deleted 1 student(s)! Failed students removed: 0 */

import java.sql.*; public class StudentCRUD { static final String URL = "jdbc:mysql://localhost:3306/college"; static final String USER = "root"; static final String PASS = "password"; static Connection connect() throws Exception { Class.forName("com.mysql.cj.jdbc.Driver"); return DriverManager.getConnection(URL, USER, PASS); } // CREATE — Insert new student static void insert(String name, int marks, String city) throws Exception { try (Connection c = connect(); PreparedStatement ps = c.prepareStatement( "INSERT INTO students(name,marks,city) VALUES(?,?,?)")) { ps.setString(1,name); ps.setInt(2,marks); ps.setString(3,city); System.out.println("✓ Inserted: " + name + " (" + ps.executeUpdate() + " row)"); } } // READ — Display all students static void readAll() throws Exception { try (Connection c = connect(); Statement s = c.createStatement(); ResultSet rs = s.executeQuery("SELECT * FROM students ORDER BY id")) { System.out.println("\nID | Name | Marks | City"); System.out.println("---+------------+-------+----------"); while (rs.next()) System.out.printf("%-3d| %-10s | %-5d | %s%n", rs.getInt("id"), rs.getString("name"), rs.getInt("marks"), rs.getString("city")); } } // UPDATE — Modify marks static void update(int id, int newMarks) throws Exception { try (Connection c = connect(); PreparedStatement ps = c.prepareStatement( "UPDATE students SET marks=? WHERE id=?")) { ps.setInt(1,newMarks); ps.setInt(2,id); int r = ps.executeUpdate(); System.out.println(r>0 ? "✓ Updated ID "+id+" → marks="+newMarks : "✗ ID not found"); } } // DELETE — Remove a student static void delete(int id) throws Exception { try (Connection c = connect(); PreparedStatement ps = c.prepareStatement( "DELETE FROM students WHERE id=?")) { ps.setInt(1,id); int r = ps.executeUpdate(); System.out.println(r>0 ? "✓ Deleted ID "+id : "✗ ID not found"); } } public static void main(String[] args) throws Exception { System.out.println("=== Student Management System ===\n"); insert("Ankush", 92, "Ludhiana"); insert("Simran", 88, "Chandigarh"); readAll(); update(1, 95); delete(4); readAll(); } } /* Output: === Student Management System === ✓ Inserted: Ankush (1 row) ✓ Inserted: Simran (1 row) ID | Name | Marks | City ---+------------+-------+---------- 1 | Raj | 85 | Delhi 2 | Priya | 92 | Mumbai 3 | Amit | 78 | Bangalore 4 | Neha | 65 | Ludhiana 5 | Ankush | 92 | Ludhiana 6 | Simran | 88 | Chandigarh ✓ Updated ID 1 → marks=95 ✓ Deleted ID 4 ID | Name | Marks | City 1 | Raj | 95 | Delhi 2 | Priya | 92 | Mumbai 3 | Amit | 78 | Bangalore 5 | Ankush | 92 | Ludhiana 6 | Simran | 88 | Chandigarh */