The Java Language Specification, Third Edition

CLASSES Method Throws 8.4.6
• If R 1 is void then R 2 is void.
DISCUSSION
The notion of return-type substitutability summarizes the ways in which return types may
vary among methods that override each other.
Note that this definition supports covariant returns - that is, the specialization of the
return type to a subtype (but only for reference types).
Also note that unchecked conversions are allowed as well. This is unsound, and
requires an unchecked warning whenever it is used; it is a special allowance is made to
allow smooth migration from non-generic to generic code.
8.4.6 Method Throws
A throws clause is used to declare any checked exceptions (§11.2) that can result
from the execution of a method or constructor:
Throws:
throws ExceptionTypeList
ExceptionTypeList:
ExceptionType
ExceptionTypeList , ExceptionType
ExceptionType:
ClassType
TypeVariable
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.
For each checked exception that can result from execution of the body of a
method or constructor, a compile-time error occurs unless that exception type or a
supertype of that exception type is mentioned in a throws clause in the declaration
of the method or constructor.
The requirement to declare checked exceptions allows the compiler to ensure
that code for handling such error conditions has been included. Methods or constructors
that fail to handle exceptional conditions thrown as checked exceptions
will normally result in a compile-time error because of the lack of a proper exception
type in a throws clause. The Java programming language thus encourages a
DRAFT
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