Why is the combiner of the Collector interface not consistent with the overloaded collect method?

Question

There is an overload method, collect(), in interface Stream with the following signature:

 R collect(Supplier

        

Answer 1

If the former collect method receive a BinaryOperator then the following example would not compile:

ArrayList list = stream.collect(ArrayList::new, 
                                     ArrayList::add,
                                     ArrayList::addAll);

In this case the compiler could not infer the return type of the combiner and would give a compilation error.

So if this version of collect method was consistent with the Collector interface then it would promote a more complex use of this version of collect method, that was not intended.