throw vs throws in Java — Keyword, Clause, and When to Use Each

The quick way to keep them straight: throw is an action, throws is a declaration.

`throw` — the statement

• Appears inside a method body: throw new IllegalArgumentException("negative amount")
• Actually raises one exception instance per statement
• Works for both checked and unchecked — any Throwable

`throws` — the clause

• Appears on the method signature: void save() throws IOException, SQLException
• Declares checked exceptions that can propagate out of the method
• Unchecked exceptions don't need to be listed — it's legal but pointless
• Forces callers to either catch those exceptions or add them to their own throws

Override rule

• A subclass override can throw the same checked exceptions, narrower subtypes, or nothing at all — never broader or unrelated types
• This preserves Liskov substitutability so callers coded against the parent don't get surprise checked exceptions

Java 7+ precise rethrow

• catch (Exception e) { throw e; } no longer forces throws Exception on the method
• The compiler tracks which specific checked types the try block could produce, so a narrow throws clause still compiles
• Requires the caught variable to be effectively final

Recommendation: Keep throws clauses as narrow as possible — they're part of the API contract and every widening forces every caller to handle more. Use throw to enforce preconditions with unchecked exceptions (argument validation) and to raise domain-specific checked exceptions only when callers genuinely have a recovery path.