Java 5 generic does not work

Question

In coding with java 5, I found I could not use Java 5 generic for all cases. For example, JAAS define a LoginModule interface as following
boolean abort()
boolean commit()
void initialize(Subject subject, CallbackHandler callbackHandler, Map<String,?> sharedState, Map<String,?> options)
Initialize this LoginModule.
boolean login()
boolean logout()
In initialize method, the login module should hold the reference to sharedState parameter and in its login method, the module put values into sharedState object to allow other login modules to share states. For example, If I would like to share password with other module, I should be able to do the following
sharedState.put("javax.security.auth.login.password", password);
But the java 5 compiler, says I can't put value into the sharedState map since ? is a wildtype.
Any one can tell me how to put values into the map Map<String, ?>.
Or If java has some good solution for this.
thanks in advance.
hao

Answer 1

minghao wrote:
I agree with you. If the semantics of java generic ? is not reworked, then the login module interface definition is not right.More precisely: if neither the semantics of ? nor the LoginModule interface is changed then the LoginModule interface doesn't make a lot of sense as it is.
But I think the semantics of java generic ? should be reworked.Why? Simply because a single interface is ill-designed?
If we changed the semantics of Map<String, ?> to allow .put() to be called, then a lot of code that depends on that semantics would break.
And if you want a Map from String to any object type, then simply use a Map<String, Object>. That's what it's there for.
It should loose some restrictiions if there's some type explicitly defined, such as Map<String, ?> if Key's type is explicitly defined, then the value could be added by using wildcard.I don't really get what you want. But I think you need to get a deeper understanding of generics. The two parameters of the Map interface (K and V, if I remember correctly) are completely unrelated.
You could give the same example with Collection<?>: It doesn't make any guarantees about the type it returns (i.e. it returns plain Objects) and doesn't accept any calls to add() because you can't possibly fullfil the type-requirements of the wildcard type.
Those are perfectly acceptable, fine and useful semantics. I see no need to change that.