What's the difference between throw and throws?

These are easily confused by name, but serve completely different roles:

• throw: a statement, used inside a method body, that actually raises (throws) a specific exception instance at that point:

void validate(int age) {
    if (age < 0) {
        throw new IllegalArgumentException("age cannot be negative"); // throw
    }
}

• throws: part of a method's signature, declaring which checked exception types the method might propagate to its caller — it doesn't raise anything itself, it's just a declaration/contract:

void readFile(String path) throws IOException, FileNotFoundException { // throws
    // ...
}

A method can have a throws clause without ever executing a throw for that exact exception (e.g., it calls another method that declares it); conversely, a method can throw an unchecked exception without any throws declaration at all, since unchecked exceptions don't require it.

Mnemonic: throw is a verb (do it now); throws is a plural declaration (these might happen, be ready).