How do Java 8 array constructor references work?

Question

Say we have a variable of type IntFunction that returns an integer array:

IntFunction<int[]> i; 

With Java 8 generics, it is possible to initialize this variable with a constructor reference like this:

i = int[]::new 

How does the Java compiler translate this to bytecode?

I know that for other types, like String::new, it can use an invokedynamic instruction that points to the String constructor java/lang/String.<init>(...), which is just a method with a special meaning.

How does this work with arrays, seeing that there are special instructions for constructing arrays?

Answer 1

You can find out yourself by decompiling the java bytecode:

javap -c -v -p MyClass.class 

The compiler desugars array constructor references Foo[]::new to a lambda (i -> new Foo[i]), and then proceeds as with any other lambda or method reference. Here's the disassembled bytecode of this synthetic lambda:

private static java.lang.Object lambda$MR$new$new$635084e0$1(int); descriptor: (I)Ljava/lang/Object; flags: ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC Code:   stack=1, locals=1, args_size=1      0: iload_0             1: anewarray     #6                  // class java/lang/String      4: areturn        

(It's return type is Object because the erased return type in IntFunction is Object.)