[Java] Stream API / map

A method that transforms all the elements in an object

public class Fruit {
	public static void main(String[] args) {
		List<String> list = new ArrayList<>();
		List<String> ret = list.stream().map(s -> s.toUpperCase()).collect(Collectors.toList());

//The output result has uppercase elements

(.Collect (Collectors.toList ()); is attached to return as List)

** If you don't use a lambda expression, it looks like this: ** **

		List<String> ret = list.stream().map(new Function<String,String>(){
			public String apply(String s) {
				return s.toUpperCase();

map () has a Function as an argument

Interface Function <T, R> T… Argument type R ... Return type

Why can apply be used suddenly? Since there are only apply methods in the interface Function (default is ignored)

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