What is this syntax in java?

Question

I find a syntax String[]::new in this answer. but I search this in google can't find useful information.

Answer 1

This is actually a shorthand for a lambda, a recent addition to Java:

size -> new String[size]

which in turn is shorthand for an IntFunction:

new IntFunction<String[]> {
  @Override
  String[] apply(int size) {
    return new String[size];
  }
}

As you can see, these additions to Java 8 make the language a bit less verbose.

Answer 2

This is a method reference to a constructor. The ClassName::method is just a terser syntax for using lambda expressions that call existing methods (in this case new), as opposed to those which call anonymous methods.