java8 :: 双冒号传多个参数

‘::’是一种函数式接口的一种书写方法引用的方式

Kind	Syntax	Examples
Reference to a static method	ContainingClass::staticMethodName	Person::compareByAge MethodReferencesExamples::appendStrings
Reference to an instance method of a particular object	containingObject::instanceMethodName	myComparisonProvider::compareByName myApp::appendStrings2
Reference to an instance method of an arbitrary object of a particular type	ContainingType::methodName	String::compareToIgnoreCase String::concat
Reference to a constructor	ClassName::new	HashSet::new

The following example, MethodReferencesExamples, contains examples of the first three types of method references:

import java.util.function.BiFunction;

public class MethodReferencesExamples {

    public static <T> T mergeThings(T a, T b, BiFunction<T, T, T> merger) {
        return merger.apply(a, b);
    }

    public static String appendStrings(String a, String b) {
        return a + b;
    }

    public String appendStrings2(String a, String b) {
        return a + b;
    }

    public static void main(String[] args) {

        MethodReferencesExamples myApp = new MethodReferencesExamples();

        // Calling the method mergeThings with a lambda expression
        System.out.println(MethodReferencesExamples.
            mergeThings("Hello ", "World!", (a, b) -> a + b));

        // Reference to a static method
        System.out.println(MethodReferencesExamples.
            mergeThings("Hello ", "World!", MethodReferencesExamples::appendStrings));

        // Reference to an instance method of a particular object
        System.out.println(MethodReferencesExamples.
            mergeThings("Hello ", "World!", myApp::appendStrings2));

        // Reference to an instance method of an arbitrary object of a
        // particular type
        System.out.println(MethodReferencesExamples.
            mergeThings("Hello ", "World!", String::concat));
    }
}

官方文档

https://docs.oracle.com/javase/tutorial/java/javaOO/methodreferences.html