Method reference with a full constructor call as a lambda expression in Java

Question

I have encountered a short time ago with a competitive answer better than mine that uses a quite new method reference to me as replacement of lambda.

Stream.         


        

Answer 1

It's simply the second type: a reference to a method of a specific object, there's no additional logic behind the curtain.

Answer 2

You can replace

Stream.generate(new AtomicInteger(1)::getAndIncrement)...

with

AtomicInteger containingObject = new AtomicInteger(1);
Stream.generate(containingObject::getAndIncrement)...

i.e. this method reference falls into the second category of method references - Reference to an instance method of a particular object.

You should note that the AtomicInteger instance creation is not part of the implementation of the IntSupplier. The Java 7 equivalent would be:

AtomicInteger aint = new AtomicInteger(1);
IntStream.generate(new IntSupplier() {

    @Override
    public int getAsInt() {
        return aint.getAndIncrement();
    }
})...

.

Answer 3

Well new AtomicInteger(1) returns an instance, so it's the second one. The exact details of how this is translated are implementation specific, but it's a single instance created and this is back-ed up by the JLS 15.13.3

First, if the method reference expression begins with an ExpressionName or a Primary, this subexpression is evaluated

In plain english, the part before :: is evaluated when it's declaration is first encountered.

Your assumption how this is translated is almost correct, it's like generating an instance outside of the function itself and using that - since it is effectively final, this is permitted.