Checked vs unchecked exceptions — what’s the difference?

Deep dive

Checked exceptions are part of the method’s contract: callers must handle them (try/catch) or declare them (throws). Unchecked exceptions are not enforced by the compiler.

Rule of thumb:

• Checked: recoverable situations the caller can realistically handle (e.g., IO, missing file) — though this is debated in modern Java.
• Unchecked: programmer errors / invariant violations (NPE, IllegalArgumentException, IllegalStateException).

Practical guidance

• Avoid “throws Exception” (it hides the real contract).
• Wrap low-level exceptions at module boundaries with context (custom exceptions).
• Don’t use exceptions for normal control flow.

Common pitfalls

• Overusing checked exceptions leading to noisy boilerplate.
• Swallowing exceptions (catch and do nothing).
• Turning everything into RuntimeException without adding context/logging.