JAVA Lab Programs

1. Calculator using switch case:

import java.util.Scanner;
public class Calculator{
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Calculator");
        System.out.println("1. Addition");
        System.out.println("2. Subtraction");
        System.out.println("3. Multiplication");
        System.out.println("4. Division");
        System.out.println("5. Exit");
        System.out.println("Enter your choice: ");
        int choice = scanner.nextInt();
        switch (choice){
            case 1:
                System.out.println("Enter two numbers: ");
                int num1 = scanner.nextInt();
                int num2 = scanner.nextInt();
                int sum = num1 + num2;
                System.out.println("The sum is: "+ sum);
                break;
            case 2:
                System.out.println("Enter two numbers: ");
                int n3 = scanner.nextInt();
                int n4 = scanner.nextInt();
                int difference = n3 - n4;
                System.out.println("The difference is: "+ difference);
                break;
            case 3:
                System.out.println("Enter two numbers: ");
                int n5 = scanner.nextInt();
                int n6 = scanner.nextInt();
                int product = n5 * n6;
                System.out.println("The product is: "+ product);
                break;
            case 4:
                System.out.println("Enter two numbers: ");
                int n7 = scanner.nextInt();
                int n8 = scanner.nextInt();
                if (n8 != 0) {
                    int division = n7 / n8;
                    System.out.println("The division is: "+ division);
                } else {
                    System.out.println("Division by zero is not allowed.");
                }
                break;
            case 5:
                System.out.println("Exiting");
                System.exit(0);
            default:
                System.out.println("Invalid choice");
                break;
        }
        scanner.close();
    }
}

3. Implement parameter passing techniques

public class ParameterPassing {
    public static void main(String[] args) {
        // Pass by value
        int x = 10;
        System.out.println("Before passing by value: x = " + x);
        passByValue(x);
        System.out.println("After passing by value: x = " + x);

        // Pass by reference
        Person person = new Person("Apple");
        System.out.println("Before passing by reference: name = " + person.getName());
        passByRef(person);
        System.out.println("After passing by reference: name = " + person.getName());
    }

    public static void passByValue(int y) {
        y++;
    }

    public static void passByRef(Person person) {
        person.setName("Ball");
    }
}

class Person {
    private String name;

    public Person(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}



4. Program that read 2d array, create 1d array that contains row & col avg.
import java.util.Scanner;
public class TwoArray Avg {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the no. of rows: ");
        int rows = scanner.nextInt();
        System.out.println("Enter the no. of columns: ");
        int cols = scanner.nextInt();
        int[][] array = new int[rows][cols];
        System.out.println("Enter the values for the array");
        for(int i=0; i<rows; i++){
            for(int j=0; j<cols; j++){
                array[i][j] = scanner.nextInt();
            }
        }
        double[] rowAverages = new double[rows];
        double[] colAverages = new double[cols];
        for(int i=0; i<rows; i++){
            int rowsum = 0;
            for(int j=0; j<cols; j++){
                rowsum += array[i][j];
            }
            rowAverages[i] = (double) rowsum/cols;
        }
        for(int j=0; j<cols; j++){
            int colsum = 0;
            for(int i=0; i<rows; i++){
                colsum += array[i][j];
            }
            colAverages[j] = (double) colsum/rows;
        }
        System.out.println("Row Averages: ");
        for(int i=0; i<rows; i++){
            System.out.println("Rows"+(i+1)+":"+rowAverages[i]);
        }
        System.out.println("Column Averages: ");
        for(int j=0; j<cols; j++){
            System.out.println("Rows"+(j+1)+":"+colAverages[j]);
        }
        scanner.close();
    }
}




6. to create class called person with private instance variable name, age and country.
public class Person {
    private String name;
    private int age;
    private String country;
    public String getName(){
        return name;
    }
    public void setName(String name){
        this.name = name;
    }
    public int getAge(){
        return age;
    }
    public void setAge(int age){
        this.age = age;
    }
    public String getCountry(){
        return country;
    }
    public void setCountry(String country){
        this.country = country;
    }
    public static void main(String[] args){
        Person person = new Person();
        person.setName("xyz");
        person.setAge(19);
        person.setCountry("India");
        System.out.println("Name: " + person.getName());
        System.out.println("Age: " + person.getAge());
        System.out.println("Country: " + person.getCountry());
    }
}




7. Program for method overloading
public class Sum {
    public int sum(int x, int y) {
        return (x + y);
    }

    public int sum(int x, int y, int z) {
        return (x + y + z);
    }

    public double sum(double x, double y) {
        return (x + y);
    }

    public static void main(String[] args) {
        Sum s = new Sum();
        System.out.println(s.sum(10, 20));
        System.out.println(s.sum(30, 40, 300));
        System.out.println(s.sum(10.5, 12.5));
    }
}



8. Create class called shape with methods called getperimeter() & getArea(). create subclass called circle that overrides the getperimeter() & getArea() 
calculate the area & perimeter of a cirlce.
class shape{
    public double getPerimeter(){
        return 0.0;
    }
    public double getArea(){
        return 0.0;
    }
}
class circle extends shape{
    private double radius;
    public circle(double radius) {
        this.radius = radius;
    }

    @Override
    public double getPerimeter() {
        return 2 * Math.PI * radius;
    }

    @Override
    public double getArea() {
        return Math.PI * Math.pow(radius, 2);
    }
}
public class Main {
    public static void main(String[] args) {
        circle circle = new circle(5.0);
        System.out.println("Perimeter: " + circle.getPerimeter());
        System.out.println("Area: " + circle.getArea());
    }
}



9. Program for different methods of string class
public class StringMethods {
    public static void main(String[] args) {
        String str = "Hello world!";
        System.out.println("Character at index 0: " + str.charAt(0));
        System.out.println("String1 equals String2: " + str.equals("Hello world!"));
        System.out.println("String1 equals String2 (ignoring case): " + str.equalsIgnoreCase("hello world!"));
        System.out.println("Index of 'o': " + str.indexOf('o'));
        System.out.println("Length of the string: " + str.length());
        System.out.println("String after replacing 'world' with 'Java': " + str.replace("world", "Java"));
        System.out.println("Substring from index 6 to 10: " + str.substring(6, 11));
        System.out.println("String in lowercase: " + str.toLowerCase());
        System.out.println("String in uppercase: " + str.toUpperCase());
        String strwithwhitespace = " Hello world! ";
        System.out.println("String with whitespace: '" + strwithwhitespace + "'");
        System.out.println("String after trimming whitespace: '" + strwithwhitespace.trim() + "'");
    }
}



10. Program to create an abstract class Animal with an abstract method called sound(). create subclasses lion & tiger that extend the Animal class & implement the sound() method to make a specific sound for each animal.
abstract class Animal{
    abstract void Sound();
}
class Lion extends Animal{
    @Override
    void Sound() {
        System.out.println("Roar!");
    }
}
class Tiger extends Animal{
    @Override
    void Sound() {
        System.out.println("Grow!");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal lion = new Lion();
        lion.Sound();
        Animal tiger = new Tiger();
        tiger.Sound();
    }
}



12. Program to implement multiple inhertance with the help of interface.
interface Interface1{
    void method1();
}
interface Interface2{
    void method2();
}
class Myclass implements Interface1, Interface2{
    public void method1() {
        System.out.println("This is method1");
    }

    public void method2() {
        System.out.println("This  is method2");
    }
}

public class Main {
    public static void main(String[] args) {
        Myclass myclass = new Myclass();
        myclass.method1();
        myclass.method2();
    }
}



14. Program to input name & age of a person & throws a user defined exception if entered age is negative
import java.util.Scanner;

public class UserDefinedException {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter your name: ");
        String name = scanner.nextLine();
        System.out.println("Enter your age: ");
        int age = scanner.nextInt();
        try {
            if (age < 0) {
                throw new InvalidAgeException("Age can't be negative");
            }
        } catch (InvalidAgeException e) {
            System.out.println(e.getMessage());
            return;
        }
        System.out.println("Hello " + name + ", you are " + age + " years old");
    }
}

class InvalidAgeException extends Exception {
    public InvalidAgeException(String message) {
        super(message);
    }
}



15. Program to create  & access a user defined package.
Myclass.java:
package com.example.mypackage;

public class Myclass {
    public void MyMethod() {
        System.out.println("This is my method!");
    }
}

Main.java:
import com.example.mypackage.Myclass;
public class Main {
    public static void main(String[] args) {
        Myclass myclass = new Myclass();
        myclass.MyMethod();
    }
}



16. Program that creates 2 threads. First thread prints the numbers from 1 to 10 & other thread prints the numbers from 10 to 1.
public class NumberPrinting{
    public static void main(String[] args) {
        Thread ascendingThread = new Thread(new Runnable() {
            @Override
            public void run() {
                Thread.currentThread().setName("Ascending Thread");
                for(int i=1; i<=10; i++){
                    System.out.println("Ascending: " + i);
                }
            }
        });
        Thread descendingThread = new Thread(new Runnable() {
            @Override
            public void run() {
                Thread.currentThread().setName("Descending Thread");
                for(int i=10; i>=1; i--){
                    System.out.println("Descending: " + i);
                }
            }
        });
        ascendingThread.start();
        descendingThread.start();
        try{
            ascendingThread.join();
            descendingThread.join();
        }catch (InterruptedException e){
            System.out.println("Thread execution interrupted: " + e.getMessage());
            Thread.currentThread().interrupt();
        }
        System.out.println("Both threads have completed thier execution.");
    }
}



18. Program that works as a simple calculator. Use a grid layout to arrange buttons for the digits & for the +, -, *, % operations. Add a text field to display the result. Handle any possible exceptions like divide by zero.
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class SimpleCalculator extends JFrame implements ActionListener {
    private JTextField display;
    private StringBuilder currentInput;
    private double result;
    private String lastOperator;

    public SimpleCalculator() {
        setTitle("Simple Calculator");
        setSize(400, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        display = new JTextField();
        display.setEditable(false);
        display.setHorizontalAlignment(JTextField.RIGHT);
        display.setFont(new Font("Arial", Font.BOLD, 20));
        currentInput = new StringBuilder();
        result = 0;
        lastOperator = " ";

        JPanel panel = new JPanel();
        panel.setLayout(new GridLayout(5, 4));

        String[] buttons = {
                "7", "8", "9", "/",
                "4", "5", "6", "*",
                "1", "2", "3", "-",
                "0", ".", "=", "+",
                "c"
        };

        for (String text : buttons) {
            JButton button = new JButton(text);
            button.setFont(new Font("Arial", Font.BOLD, 20));
            button.addActionListener(this);
            panel.add(button);
        }

        add(display, BorderLayout.NORTH);
        add(panel, BorderLayout.CENTER);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();
        if ("0123456789.".contains(command)) {
            currentInput.append(command);
            display.setText(currentInput.toString());
        } else if ("+-*/".contains(command)) {
            calculate();
            lastOperator = command;
            currentInput.setLength(0);
        } else if ("=".equals(command)) {
            calculate();
            display.setText(String.valueOf(result));
            lastOperator = " ";
            currentInput.setLength(0);
        } else if ("c".equals(command)) {
            result = 0;
            currentInput.setLength(0);
            display.setText(" ");
            lastOperator = " ";
        }
    }

    private void calculate() {
        double currentNumber = Double.parseDouble(currentInput.toString());
        switch (lastOperator) {
            case " ":
                result = currentNumber;
                break;
            case "+":
                result += currentNumber;
                break;
            case "-":
                result -= currentNumber;
                break;
            case "*":
                result *= currentNumber;
                break;
            case "/":
                if (currentNumber == 0) {
                    JOptionPane.showMessageDialog(this, "Error: Division by Zero", "ERROR", JOptionPane.ERROR_MESSAGE);
                } else {
                    result /= currentNumber;
                }
                break;
        }
        display.setText(String.valueOf(result));
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            SimpleCalculator calculator = new SimpleCalculator();
            calculator.setVisible(true);
        });
    }
}



19. Program that handles all mouse events & shows the event name at the center of the window when a mouse event is fired.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class MouseEventDemo extends JFrame implements MouseListener, MouseMotionListener {
    private String eventText = " ";

    public MouseEventDemo() {
        setTitle("Mouse Event Demo");
        setSize(400, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        addMouseListener(this);
        addMouseMotionListener(this);
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        g.setFont(new Font("Arial", Font.BOLD, 20));
        FontMetrics fm = g.getFontMetrics();
        int x = (getWidth() - fm.stringWidth(eventText)) / 2;
        int y = (getHeight() - fm.getHeight()) / 2 + fm.getAscent();
        g.drawString(eventText, x, y);
    }

    @Override
    public void mouseClicked(MouseEvent e) {
        eventText = "Mouse Clicked";
        repaint();
    }

    @Override
    public void mousePressed(MouseEvent e) {
        eventText = "Mouse Pressed";
        repaint();
    }

    @Override
    public void mouseReleased(MouseEvent e) {
        eventText = "Mouse Released";
        repaint();
    }

    @Override
    public void mouseEntered(MouseEvent e) {
        eventText = "Mouse Entered";
        repaint();
    }

    @Override
    public void mouseExited(MouseEvent e) {
        eventText = "Mouse Exited";
        repaint();
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        eventText = "Mouse Dragged";
        repaint();
    }

    @Override
    public void mouseMoved(MouseEvent e) {
        eventText = "Mouse Moved";
        repaint();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            MouseEventDemo frame = new MouseEventDemo();
            frame.setVisible(true);
        });
    }
}



20. Program to create a frame window that responds to key strokes.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class keyEventDemo extends JFrame implements KeyListener {
    private String keyText = " ";

    public keyEventDemo() {
        setTitle("Key Event Demo");
        setSize(400, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        addKeyListener(this);
        setFocusable(true);
        setFocusTraversalKeysEnabled(false);
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        g.setFont(new Font("Arial", Font.BOLD, 20));
        FontMetrics fm = g.getFontMetrics();
        int x = (getWidth() - fm.stringWidth(keyText)) / 2;
        int y = (getHeight() - fm.getHeight()) / 2 + fm.getAscent();
        g.drawString(keyText, x, y);
    }

    @Override
    public void keyTyped(KeyEvent e) {
        keyText = "Key Typed: " + e.getKeyChar();
        repaint();
    }

    @Override
    public void keyPressed(KeyEvent e) {
        keyText = "Key Pressed: " + KeyEvent.getKeyText(e.getKeyCode());
        repaint();
    }

    @Override
    public void keyReleased(KeyEvent e) {
        keyText = "Key Released: " + KeyEvent.getKeyText(e.getKeyCode());
        repaint();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            keyEventDemo frame = new keyEventDemo();
            frame.setVisible(true);
        });
    }
}