Java exceptions contract of Iterator remove -

i'm implementing iterator utilises iterator, of not know, whether supports remove() method or not.

consider following edge case: underlying iterator not support remove() , iterator next() has not yet been called.

do violate interface contract, if remove() throws – in situation – illegalstateexception instead of unsupportedoperationexception?
(as next() called, underlying remove() can called, throw appropriate unsupportedoperationexception.)

if so, how refactor code check whether underlying iterator supports remove() or not?

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an example:

<t> iterator<t> getsetviewiterator(collection<t> collection) {      iterator<t> uniqueitr = new hashset<>(collection).iterator();      return new iterator<t>() {         private t current = null;         private boolean hasremoved = true;          @override         public boolean hasnext() {             return uniqueitr.hasnext();         }          @override         public t next() {             if(!hasnext())                 throw new nosuchelementexception();              hasremoved = false;              return current = uniqueitr.next();         }          @override         public void remove() {             if(hasremoved)                 throw new illegalstateexception();              for(iterator<t> iterator = collection.iterator(); iterator.hasnext();) {                 if(iterator.next().equals(current))                     iterator.remove();             }              hasremoved = true;         }     }; } 

(for our purposes can assume, passed collection not contain null.)

per documentation linked to, both exceptions acceptable remove method, , situation of calling remove prior next explicitly mentioned, , allows throwing illegalstateexception.

for iterator not support remove, throwing unsupportedoperationexception valid throwing illegalstateexception in illegal states (remove before next, second remove after next), , throwing other exception in valid states (first remove after next). both exceptions applicable call in invalid state - because state invalid , operation unsupported.

your wrapping iterator works right - checks invalid state, , delegates inner iterator, may throw unsupported operation exception. iterator not need know whether inner iterator supports remove because, noted above, in illegal state both exceptions valid responses.