9.1. Try-Catch Blocks

Exception handling is a mechanism to handle runtime errors so that the normal flow of the application can be maintained. The try-catch block is the fundamental construct for handling exceptions in Java.

What are Exceptions?

Exceptions are events that occur during the execution of programs that disrupt the normal flow of instructions. In Java, exceptions are objects that wrap an error event.

Basic Try-Catch Syntax

try {
    // Code that might throw an exception
    riskyOperation();
} catch (ExceptionType name) {
    // Code to handle the exception
    handleError();
}

Try Block

The try block contains code that might throw an exception. If an exception occurs within the try block, the rest of the code in the try block is skipped.

try {
    System.out.println("Before risky operation");
    int result = 10 / 0;  // This will throw ArithmeticException
    System.out.println("After risky operation");  // This line won't execute
} catch (ArithmeticException e) {
    System.out.println("Exception caught!");
}

Catch Block

The catch block contains exception handling code. It's executed only if an exception of the specified type occurs in the try block.

try {
    FileReader file = new FileReader("nonexistent.txt");
} catch (FileNotFoundException e) {
    System.out.println("File not found: " + e.getMessage());
}

Exception Object

The exception object contains information about the error:

try {
    int[] numbers = {1, 2, 3};
    System.out.println(numbers[5]);
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Message: " + e.getMessage());
    System.out.println("Class: " + e.getClass().getName());
    e.printStackTrace();  // Prints stack trace to console
}

Complete Example

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

        try {
            System.out.print("Enter numerator: ");
            int numerator = scanner.nextInt();

            System.out.print("Enter denominator: ");
            int denominator = scanner.nextInt();

            int result = numerator / denominator;
            System.out.println("Result: " + result);

        } catch (ArithmeticException e) {
            System.out.println("Error: Division by zero is not allowed");

        } catch (java.util.InputMismatchException e) {
            System.out.println("Error: Please enter valid integers");

        } finally {
            scanner.close();
        }
    }
}

Key Points

• Try block must be followed by at least one catch or finally block
• Multiple catch blocks can handle different exception types
• Exception handling prevents program termination due to runtime errors
• Always handle specific exceptions rather than using generic Exception class