Unit 1: Java programming implementation

• Single-file launch: java Program.java compiles and runs in one step (Java 11+).

javapublic class MathDemo {
    public static void main(String[] args) {
        int a = 17, b = 5;
        System.out.println("Sum " + (a + b) + " Quotient " + (a / b) + " Remainder " + (a % b));
        System.out.println("a > b ? " + (a > b) + "  a & b = " + (a & b) + "  a << 2 = " + (a << 2));
        System.out.println(Math.sqrt(144) + " " + Math.pow(2, 10) + " " + Math.abs(-7));
        System.out.println(Math.max(a, b) + " " + Math.round(4.6) + " " + Math.ceil(4.1) + " " + Math.floor(4.9));
        double r = 7;
        System.out.printf("Area of circle = %.2f%n", Math.PI * r * r);
        System.out.println("Random 1–6: " + (int) (Math.random() * 6 + 1));
    }
}

javaimport java.util.Scanner;
public class Loops {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int n = sc.nextInt();
        System.out.println(n % 2 == 0 ? "Even" : "Odd");

        long fact = 1;                                   // factorial
        for (int i = 2; i <= n; i++) fact *= i;
        System.out.println("Factorial = " + fact);

        int t = n, arm = 0, digits = String.valueOf(n).length();   // Armstrong check
        while (t > 0) { arm += Math.pow(t % 10, digits); t /= 10; }
        System.out.println(arm == n ? "Armstrong" : "Not Armstrong");

        for (int i = 1; i <= 4; i++) {                   // pattern
            for (int j = 1; j <= i; j++) System.out.print(j + " ");
            System.out.println();
        }
    }
}

javaclass BankAccount {
    private String holder; private double balance;
    BankAccount(String h, double b) { holder = h; balance = b; }
    void deposit(double amt) { balance += amt; }
    boolean withdraw(double amt) { if (amt > balance) return false; balance -= amt; return true; }
    void show() { System.out.println(holder + " : Rs " + balance); }
}
class Savings extends BankAccount {                      // inheritance
    double rate;
    Savings(String h, double b, double r) { super(h, b); rate = r; }
    @Override void show() { super.show(); System.out.println("Interest rate " + rate + "%"); }
}
public class BankDemo {
    public static void main(String[] args) {
        BankAccount acc = new Savings("Riya", 10000, 3.5);
        acc.deposit(2500);
        System.out.println(acc.withdraw(20000) ? "Done" : "Insufficient balance");
        acc.show();                                       // runtime polymorphism
    }
}

javaimport java.util.*;
public class ArrStr {
    public static void main(String[] args) {
        int[] a = {34, 12, 78, 5, 61};
        Arrays.sort(a);
        System.out.println(Arrays.toString(a) + " max " + a[a.length - 1]);

        int[][] m = {{1, 2}, {3, 4}}, n = {{5, 6}, {7, 8}}, p = new int[2][2];
        for (int i = 0; i < 2; i++)                      // matrix multiplication
            for (int j = 0; j < 2; j++)
                for (int k = 0; k < 2; k++) p[i][j] += m[i][k] * n[k][j];
        System.out.println(Arrays.deepToString(p));      // [[19, 22], [43, 50]]

        String s = "madam";
        System.out.println(new StringBuilder(s).reverse().toString().equals(s) ? "Palindrome" : "No");
        String[] names = {"Kabir", "Aman", "Simran"};
        Arrays.sort(names);                               // alphabetical order
        System.out.println(String.join(", ", names));

        Vector<String> v = new Vector<>(List.of("C", "C++"));
        v.add("Java"); v.insertElementAt("Python", 0); v.removeElement("C");
        System.out.println(v + " size " + v.size());
    }
}

java// shapes/Shape.java
package shapes;
public interface Shape { double area(); default String name() { return "Shape"; } }

// shapes/Circle.java
package shapes;
public class Circle implements Shape {
    double r; public Circle(double r) { this.r = r; }
    public double area() { return Math.PI * r * r; }
    public String name() { return "Circle"; }
}

// Main.java
import shapes.*;
public class Main {
    public static void main(String[] args) {
        Shape s = new Circle(3);
        System.out.printf("%s area %.2f%n", s.name(), s.area());
    }
}

bashjavac -d . shapes/Shape.java shapes/Circle.java Main.java
java Main

javaimport java.util.Scanner;
class AgeException extends Exception { AgeException(String m) { super(m); } }
public class ExDemo {
    static void checkAge(int age) throws AgeException {
        if (age < 18) throw new AgeException("Not eligible to vote");
        System.out.println("Eligible");
    }
    public static void main(String[] args) {
        try {
            int[] x = new int[2];
            System.out.println(10 / Integer.parseInt(args.length > 0 ? args[0] : "0"));
            x[3] = 1;
        } catch (ArithmeticException e) { System.out.println("Divide by zero");
        } catch (ArrayIndexOutOfBoundsException e) { System.out.println("Bad index");
        } finally { System.out.println("finally runs"); }
        try { checkAge(16); } catch (AgeException e) { System.out.println(e.getMessage()); }
    }
}

• Applets no longer run in browsers; run applet code with appletviewer on JDK 8, or draw the same output in a Frame as below.

javaimport java.awt.*;
public class Drawing extends Frame {
    Drawing() { setTitle("Graphics"); setSize(420, 320); setVisible(true); }
    public void paint(Graphics g) {
        g.setColor(Color.red);    g.drawLine(30, 60, 380, 60);
        g.setColor(Color.blue);   g.fillRect(30, 80, 100, 60);
        g.setColor(Color.green);  g.fillOval(150, 80, 80, 80);
        g.setColor(Color.black);  g.drawArc(250, 80, 100, 100, 0, 180);
        g.drawPolygon(new int[]{60, 110, 10}, new int[]{200, 280, 280}, 3);
        g.drawString("Java Graphics Lab", 150, 260);
    }
    public static void main(String[] a) { new Drawing(); }
}

javaimport java.awt.*;
import java.awt.event.*;
public class LoginForm extends Frame implements ActionListener {
    TextField user = new TextField(15), pass = new TextField(15);
    Label msg = new Label("                         ");
    Button login = new Button("Login");
    LoginForm() {
        super("Login");
        setLayout(new GridLayout(4, 2, 5, 5));
        pass.setEchoChar('*');
        add(new Label("User")); add(user); add(new Label("Password")); add(pass);
        add(login); add(msg);
        login.addActionListener(this);
        addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { dispose(); } });
        setSize(320, 160); setVisible(true);
    }
    public void actionPerformed(ActionEvent e) {
        msg.setText(user.getText().equals("admin") && pass.getText().equals("sbs@123") ? "Welcome" : "Invalid");
    }
    public static void main(String[] a) { new LoginForm(); }
}

• Also practise: a calculator with GridLayout buttons, a MouseListener program showing click coordinates, and a KeyListener program counting typed characters.

javaimport java.io.*;
public class FileDemo {
    public static void main(String[] args) throws IOException {
        try (PrintWriter pw = new PrintWriter(new FileWriter("marks.txt"))) {
            pw.println("Aman 78"); pw.println("Riya 91"); pw.println("Kabir 66");
        }
        int total = 0, count = 0;
        try (BufferedReader br = new BufferedReader(new FileReader("marks.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                total += Integer.parseInt(line.split(" ")[1]); count++;
            }
        }
        System.out.println("Average = " + (double) total / count);
        File f = new File("marks.txt");
        System.out.println(f.getName() + " " + f.length() + " bytes, exists: " + f.exists());
    }
}

• Programs on arithmetic, relational, logical and bitwise operators and Math functions.
• Even–odd, largest of three, grade using if-else and switch; factorial, Fibonacci, prime, Armstrong and patterns using loops.
• Classes with constructors, overloading, static members; inheritance and overriding.
• Array sorting and searching, matrix addition and multiplication, string palindrome and sorting names, Vector operations.
• Interfaces and user-defined packages.
• Built-in and user-defined exceptions with try, catch, finally, throw and throws.
• Applet or Frame drawing shapes and a bar chart; passing parameters to an applet.
• AWT forms, calculator, mouse and key events.
• Reading, writing and copying files; RandomAccessFile updates.