Exception Handling

The Big Picture

Exceptions handle runtime errors without crashing the program. When something goes wrong, Java throws an exception object that travels up the call stack until caught.

• Checked exceptions must be declared or caught
• Unchecked exceptions (runtime) don't require handling
• try/catch/finally is the core mechanism

How It Works

When thrown, the JVM unwinds the stack looking for a match.

• try blocks contain risky code
• catch handles specific exception types
• finally normally runs after try/catch (cleanup resources)
• Checked: IOException must be caught or declared throws
• Unchecked: NullPointerException extends RuntimeException

In the Java Landscape

Java 7+ try-with-resources auto-closes AutoCloseable objects.

• Multi-catch: catch (IOException | SQLException e)
• Suppressed exceptions accessible via getSuppressed()
• Optional (Java 8) reduces null-related exceptions
• Helpful NPE messages added in Java 14
• Pattern matching reduces ClassCastException risk

Pitfalls and Best Practices

• Catch specific types; broad Exception only at boundaries, never Throwable
• Don't swallow exceptions - always log or rethrow
• Avoid exceptions for control flow (expensive stack traces)
• Include context in messages: what failed and why
• Use unchecked for bugs, checked for recoverable issues
• Prefer try-with-resources over manual finally blocks