What is the use of "System.out::println" in Java 8

Question

I saw a code in java 8 to iterate a collection.

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
numbers.forEach(System.out::println);

What is the functionality of System.out::println ? And how the above code can iterate through the List.

And what is the use of the operator :: , Where else we can use this operator ?

Konstantin Yovkov · Accepted Answer · 2015-06-24T07:27:22.170

92

It's called a "method reference" and it's a syntactic sugar for expressions like this:

numbers.forEach(x -> System.out.println(x));

Here, you don't actually need the name x in order to invoke println for each of the elements. That's where the method reference is helpful - the :: operator denotes you will be invoking the println method with a parameter, which name you don't specify explicitly:

numbers.forEach(System.out::println);

edited Jun 24 '15 at 07:27

answered Jun 24 '15 at 07:25

Konstantin Yovkov

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so what are other use of the `::` operator ? – prime Jun 24 '15 at 07:27
what do you mean with *other use*? – Konstantin Yovkov Jun 24 '15 at 07:29
I mean where else it can be used ? – prime Jun 24 '15 at 07:30
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It's used only for method references. – Konstantin Yovkov Jun 24 '15 at 07:31
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That lambda expression is [not exactly equivalent to the method reference](http://stackoverflow.com/a/28025717/2711488) – Holger Jun 24 '15 at 08:32
How will I use X as variable to pass to other method – Ravi Parekh Jun 07 '17 at 07:38
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commenting quite late but what is the REAL advantage ? is this not making the code less readable and less maintainable ? – satish marathe Aug 07 '18 at 09:31
So in other words, **method references are syntatic sugar for lambda expressions**. Is that correct? – Sebastian Nielsen Nov 02 '19 at 10:20

What is the use of "System.out::println" in Java 8

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