java - Making assumptions about type parameters? -

i want subclass iterator i'll call fooiterator. code looks this:

public class fooiterator<e> implements iterator<e> {   public fooiterator(collection<bar> bars) {     inneriterator = bars.iterator();   }    @override   public boolean hasnext() {     return inneriterator.hasnext();   }    @suppresswarnings("unchecked")   @override   public e next() {     bar bar = inneriterator.next();     return new e(bar);   }    @override   public void remove() {     throw new unsupportedoperationexception("don't remove fooiterator!");   }    private iterator<bar> inneriterator; } 

...except, of course, doesn't work because can't instantiate new e bar.

i ever use e has constructor takes bar. there way "prove" compiler, or throw runtime error if e doesn't have appropriate constructor?

or perhaps i'm not using right design pattern here? i've been doing lot of c++ recently, , feel might approaching wrong way.

this convoluted approach work , type safe (solutions using reflection won't). consists in delegating construction of e bar separate class. have barconverter interface:

interface barconverter<e> {     e convert (bar bar); } 

then class become:

public class fooiterator<e> implements iterator<e> {      public fooiterator(collection<bar> bars, barconverter<e> converter) {         inneriterator = bars.iterator();         this.converter = converter;     }      @override     public e next() {         bar bar = inneriterator.next();         return converter(bar);     } }