When do method references work?

Question

Method references don't work with non-static methods AFAIK. I tried using them in the following way

Arrays.stream(new Integer[] {12,321,312}).map(Integer::toString).forEach(System.out::println);

Which resulted in the compilation error as seen in the link.

Problem
While using AssertJ library, I used something like this,

AbstractObjectAssert<?, Feed> abstractObjectAssertFeed2 = assertThat(feedList.get(2));
abstractObjectAssertFeed2.extracting(Feed::getText).isEqualTo(new Object[] {Constants.WISH+" HappyLife"});

where Feed is a noun and getText is a getter method and not static, but it worked fine without compilation error or any error which puzzled me.

Am I missing something about how method references work?

Answer 1

This is invalid for a different reason.

Basically there are two toString implementations in Integer.

static toString(int)

and

/*non- static*/ toString()

Meaning you could write your stream like this:

 Arrays.stream(new Integer[] { 12, 321, 312 })
       .map(i -> i.toString(i))
       .forEach(System.out::println);

Arrays.stream(new Integer[] { 12, 321, 312 })
       .map(i -> i.toString())
       .forEach(System.out::println);

Both of these qualify as a method reference via Integer::toString. The first one is a method reference to a static method. And the second is Reference to an instance method of an arbitrary object of a particular type.

Since they both qualify the compiler does not know which to choose.