Java asserts in interfaces?

[Ken]

Hi. Does anyone know if java asserts can be applied to interface
operations? I ask this in the context of verifying contracts. The
idea is that you'd want to use asserts to define pre and post
conditions for each operation in the interface. Then these asserts
would be automatically applied to any class that implemented the
interface. This would avoid having to physically include the same
assert code in every class that implemented the interface. This is
the same idea behind allowing an interface to have its exceptions
identified--namely, to guanrantee that each implementation will throw
the exceptions associated with the interface.

Thanks for any input,

Ken

 

[Manish Hatwalne]

I don't think it would be allowed.
assert is part of implementation whereas interface by definition does not
have any implementation details in it.

- Manish

 

[Michael Borgwardt]

Hi. Does anyone know if java asserts can be applied to interface
operations?

No.

What you're looking for is part of the programming philosophy called "design by contract".
There are languages that support it fully - Java is not among them.

 

[Roedy Green]

What you're looking for is part of the programming philosophy called "design by contract".
There are languages that support it fully - Java is not among them.

The tricky part of design by contract is the way classes inherit the
contracts of the base, and can tighten them, but not loosen them.


see http://mindprod.com/jgloss/objectorientedsoftware.html

 

[Timo Kinnunen]

Hi. Does anyone know if java asserts can be applied to interface
operations? I ask this in the context of verifying contracts.

No, but you can simulate it to some extent by providing a concrete wrapper
class which implements the interface and checks the contract before and
after forwarding to the real instance. Then wrap any untrusted incoming
classes into it at your module's boundary.

 

[Guus Bosman]

Hi,

As the other poster pointed out, Java interfaces do not support the assert
keyword.

Additionally, the Java assert keyword should not be used to verify
pre-conditions in public methods.

http://java.sun.com/j2se/1.4.2/docs/guide/lang/assert.html#preconditions

For private methods it's okay to use ''assert'', but not for public ones
(IllegalArgumentExceptions and NullPointerExceptions should be thrown there,
not AssertionFailedErrors). And obviously, in Java Interfaces only public
methods exist.

Regards,
Guus Bosman
http://www.guusbosman.nl