Exception Handling in Java

An exception is an event, which occurs during the execution of a program, that disrupts the normal flow of the program’s instructions. Java uses try, catch, throw and finally to handle exceptions.

Throwing an Exception

You can manually throw an exception using throw, and declare it using throws in the method signature.

double division(int divisor, int dividend) throws Exception {
    if (divisor == 0)
        throw new Exception("can't divide by zero");

    return (divisor * 1.0 / dividend);
}

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Try and Catch Blocks

When there’s a risk of an exception occurring, wrap the risky code in a try block and handle specific exceptions using catch.

public class Example {
    public static void main(String[] args) {
        try {
            int result = 10 / 0; // This causes ArithmeticException
            System.out.println(result);
        } catch (ArithmeticException e) {
            System.out.println("Error: Cannot divide by zero");
        }

        System.out.println("Program continues...");
    }
}

✅ Output:

Error: Cannot divide by zero
Program continues...

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Finally Block

finally is used to write code that must run regardless of whether an exception occurred or not (like closing a file or database connection).

try {
    int[] arr = new int[2];
    arr[3] = 5; // This causes ArrayIndexOutOfBoundsException
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Index out of range!");
} finally {
    System.out.println("This will always run.");
}

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Common Exception Types

Exception Type	Description
ArithmeticException	Division by zero or bad arithmetic
NullPointerException	Accessing a method or field of null
ArrayIndexOutOfBoundsException	Accessing outside array boundaries
IOException	Input/Output errors (e.g., file not found)
FileNotFoundException	File not found when trying to read
IllegalArgumentException	Invalid method argument