Exception Handling in Java

An exception is an unwanted event during execution that disrupts the normal flow of a program. Exception handling lets the program respond to it gracefully instead of crashing.

Keywords

Keyword	Purpose
`try`	Block of code that might throw an exception
`catch`	Handles the exception
`finally`	Always executes (cleanup)
`throw`	Throws an exception explicitly
`throws`	Declares exceptions a method may throw

Java

try {
    int r = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Error: " + e.getMessage());
} finally {
    System.out.println("Finally block always runs");
}
System.out.println("Program continues...");

Error: / by zero Finally block always runs Program continues...

Checked vs Unchecked

Checked	Unchecked
Checked at compile time	Occur at runtime
`IOException`, `SQLException`	`NullPointerException`, `ArithmeticException`
Must be handled or declared	Handling optional

Custom Exception

Java

class InvalidAgeException extends Exception {
    InvalidAgeException(String msg) { super(msg); }
}

static void vote(int age) throws InvalidAgeException {
    if (age < 18) throw new InvalidAgeException("Age must be 18 or above");
    System.out.println("You can vote");
}

try { vote(15); }
catch (InvalidAgeException e) { System.out.println("Caught: " + e.getMessage()); }

Caught: Age must be 18 or above

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