Introduction

Exception handling in Java is a powerful mechanism that allows a program to handle runtime errors gracefully. Errors such as invalid input, division by zero, or file access problems can cause abnormal program termination. Java provides keywords like try, catch, throw, throws, and finally to handle exceptions effectively. This lab focuses on understanding and implementing exception handling techniques to make Java programs robust and reliable.

Objectives

The objectives of this lab are:

To understand and implement the try and multiple catch blocks
To learn how to create and use user-defined exceptions
To demonstrate the use of throw and throws keywords in Java

Program 1: Try and Multiple Catch Blocks

MultipleCatchDemo.java

import java.util.Scanner;

public class MultipleCatchDemo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        try {
            System.out.print("Enter first number: ");
            int a = sc.nextInt();

            System.out.print("Enter second number: ");
            int b = sc.nextInt();

            int result = a / b;
            System.out.println("Result: " + result);
        }
        catch (ArithmeticException e) {
            System.out.println("Error: Division by zero is not allowed.");
        }
        catch (Exception e) {
            System.out.println("Error: Invalid input.");
        }
        finally {
            System.out.println("Program execution completed.");
        }

        sc.close();
    }
}

Output:

Program 2: User-Defined Exception

`UserDefinedExceptionDemo.java`

import java.util.Scanner;

public class UserDefinedExceptionDemo {

    int balance;

    public void amountToWithdraw(int a) {
        try {
            if (a > balance) {
                throw new LessBalance(a, balance);
            }
            balance = balance - a;
            System.out.println("Amount withdrawn successfully.");
            System.out.println("Remaining balance: " + balance);
        } catch (LessBalance error) {
            System.out.println(error.getMessage());
        }
    }

    public static void main(String[] args) {
        UserDefinedExceptionDemo user = new UserDefinedExceptionDemo();
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter your balance: ");
        user.balance = sc.nextInt();

        System.out.print("Enter amount to withdraw: ");
        int a = sc.nextInt();

        user.amountToWithdraw(a);
        sc.close();
    }

    // User-defined exception
    static class LessBalance extends Exception {
        public LessBalance(int withdrawAmount, int balance) {
            super("Insufficient balance! Your balance is " + balance +
                    " but you tried to withdraw " + withdrawAmount);
        }
    }
}

Output:

Program 3: `throw` and `throws` Keyword

`ThrowThrowsDemo.java`

public class ThrowThrowsDemo {

    static void divide(int a, int b) throws ArithmeticException {
        if (b == 0) {
            throw new ArithmeticException("Cannot divide by zero");
        }
        System.out.println("Result: " + (a / b));
    }

    public static void main(String[] args) {
        try {
            divide(9, 0);
        }
        catch (ArithmeticException e) {
            System.out.println("Exception caught: " + e.getMessage());
        }
    }
}

Output:

Conclusion

In this lab, we learned how to handle runtime errors using Java’s exception handling mechanism. We implemented try with multiple catch blocks, created and used user-defined exceptions, and demonstrated the use of throw and throws keywords. Exception handling helps prevent abnormal program termination and improves the reliability and robustness of Java applications.