Exception Handling

Java splits exceptions into two kinds. Checked exceptions (like IOException) must be either caught or declared with throws — the compiler enforces this. Unchecked exceptions (RuntimeException and its subclasses, like NullPointerException) need no such declaration, and usually signal a programming mistake rather than an expected, recoverable condition.

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Can't divide by zero: " + e.getMessage());
} finally {
    System.out.println("This always runs");
}

Can't divide by zero: / by zero
This always runs

try-with-resources automatically closes a resource (like a file) even if an exception is thrown, without a manual finally:

try (var reader = new java.io.FileReader("data.txt")) {
    // use reader
} catch (java.io.IOException e) {
    System.out.println("Couldn't read file: " + e.getMessage());
}

Common mistakes

• Catching Exception (or worse, Throwable) generically "to be safe" — this also silently swallows bugs that should have crashed loudly during development. Catch the specific exception type you actually expect and know how to handle.
• An empty catch block that discards the error entirely, making a real failure invisible.

Practice

Write code that attempts to parse "abc" as an integer with Integer.parseInt, catching NumberFormatException and printing a friendly message.

try {
    int n = Integer.parseInt("abc");
} catch (NumberFormatException e) {
    System.out.println("That wasn't a valid number");
}