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Introduction

In Java, an exception is an event that interrupts the normal flow of a program. Exceptions usually occur when something unexpected happens during execution, such as dividing a number by zero or trying to access an invalid index in an array.

In simple terms, exceptions represent abnormal situations that may lead to incorrect or no result.

Example


int a = 10;

int b = 0;

System.out.println(a / b); // This will throw ArithmeticException

Since dividing a number by zero is not valid, an exception is thrown.

How to Handle Exceptions?

Java provides a robust exception handling mechanism to manage runtime errors. An exception can either be:

Handled inside the method itself using try-catch blocks.

Thrown to the caller using the throws keyword.

At some point, every exception must be handled to prevent program crashes.

Types of Exceptions in Java

Exceptions in Java are mainly divided into two categories:

Built-in Exceptions

Checked Exceptions
Unchecked Exceptions

User-Defined Exceptions

1. Built-in Exceptions

These are predefined exceptions in Java, available in the java.lang package.

a) Checked Exceptions

Also known as compile-time exceptions. These are checked by the compiler before execution. If not handled, they cause a compilation error.

Examples:

Reading from a file that does not exist → FileNotFoundException

Reading past the end of a file → EOFException


import java.io.*;

class CheckedExample {
    public static void main(String[] args) {
        try {
            FileReader fr = new FileReader("unknown.txt");
        } catch (FileNotFoundException e) {
            System.out.println("File not found!");
        }
    }
}

b) Unchecked Exceptions

Also known as runtime exceptions. These occur during execution and are not checked by the compiler.

Examples:

Accessing an invalid array index → ArrayIndexOutOfBoundsException

Dividing a number by zero → ArithmeticException


class UncheckedExample {
    public static void main(String[] args) {
        int[] arr = {10, 20, 30};
        System.out.println(arr[5]); // ArrayIndexOutOfBoundsException
    }
}

2. User-Defined Exceptions

Java allows programmers to create their own custom exceptions. This is useful