What does it mean: a sign in java? [duplicate]

Question

What does it mean: a sign in java? [duplicate]

This question is already answered here: What does the:: operator mean? (1 answer) Closed 2 years back.

I often see :: when defining a new instance, in streams, sometimes in lambda expressions. What does it mean? What does List :: stream mean?

P.S. And what is it called?

4

java lambda лямбда-выражение java-stream

Author: Anton Sorokin, 2018-08-16

Source

1 answers

score 12 · Accepted Answer

The "method reference" operator (Method Reference). In fact , it is an abbreviated entry for referring to a method from a functional interface when using a lambda.

List::stream

Is a reference to the stream() method from the List{[12 interface]}

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

The above code snippet means: 1. We initialize a stream that will have a list of numbers (Stream<List<Integer>>) 2. using flatMap we combine the list of numbers into a stream of numbers (Stream<Integer>) 3. using forEach and a reference to the println method for each element from the stream is called to display

If you speak English, a good explanation with examples is given in this answer