map 的 Java 方法引用 - IntelliJ 警告

Question

Intellij 警告这个表达式:

usersAttributes.get(user.getName()).forEach((attrName, val) -> user.addAttribute(attrName, val));

可以用方法引用代替。我该怎么做？

Answer 1

IntelliJ 是对的。你可以重写:

usersAttributes.get(user.getName()).forEach(user::addAttribute);

这种method reference叫做"Reference to an instance method of a particular object" :

The following is an example of a reference to an instance method of a particular object:

class ComparisonProvider {
     public int compareByName(Person a, Person b) {
         return a.getName().compareTo(b.getName());
     }

     public int compareByAge(Person a, Person b) {
         return a.getBirthday().compareTo(b.getBirthday());
     }
 }
 ComparisonProvider myComparisonProvider = new ComparisonProvider();
 Arrays.sort(rosterAsArray, myComparisonProvider::compareByName);

The method reference myComparisonProvider::compareByName invokes the method compareByName that is part of the object myComparisonProvider. The JRE infers the method type arguments, which in this case are (Person, Person).

在您的情况下，user::addAttribute 指的是名为 addAttribute 的方法采用两个参数，其中第一个参数与 attrName 的类型兼容> 而第二个也与 val 的类型兼容。此方法将在 user 实例上调用。