A compile-time error occurs if any ExceptionType mentioned in a throws clause is not a subtype (§4.10) of Throwable. It is permitted but not required to mention other (unchecked) exceptions in a throws clause.

A compiler for the Java programming language checks, at compile time, that a program contains handlers for checked exceptions, by analyzing which checked exceptions can result from execution of a method or constructor.

The unchecked exceptions classes are the class RuntimeException and its subclasses, and the class Error and its subclasses. All other exception classes are checked exception classes.