Denial of service via hash collisions

What particular fix would you suggest for JAVA that is not possible with current standard constraints?
I have the impression the HashMap class (and maybe a couple more classes) can be made safer because they are widely used in UI frameworks and can be easily exploited. But I don't see anything preventing the HashMap implementation from having hash algorithm changed. Also it could be easily made dynamic through the rehash() method (i.e. change algo on rehash on certain conditions).