问题描述

Sonar 告诉我用方法引用替换这个 lambda"

Sonar tells me "Replace this lambda with a method reference"

public class MyClass {

    private List<SomeValue> createSomeValues(List<Anything> anyList) {
        return anyList //
               .stream() //
               .map(anything -> createSomeValue(anything)) //
               .collect(Collectors.toList());
   }

    private SomeValue createSomeValue(Anything anything) {
        StatusId statusId = statusId.fromId(anything.getStatus().getStatusId());
        return new SomeValue(anything.getExternId(), statusId);
    }

}

这可能吗?我尝试了几件事，比如

Is this possible here? I tried several things, like

.map(MyClass::createSomeValue) //

但是我需要将方法更改为静态.而且我不是静态方法的忠实粉丝.

but I need to change the method to static then. And I am not a big fan of static methods.

SonarQube 的解释是:

Explanation of SonarQube is:

方法/构造函数引用比使用 lambda 更紧凑和可读，因此是首选.

Method/constructor references are more compact and readable than using lambdas, and are therefore preferred.

推荐答案

是的，你可以使用 this::createSomeValue:

private List<SomeValue> createSomeValues(List<Anything> anyList) {
    return anyList //
            .stream() //
            .map(this::createSomeValue) //
            .collect(Collectors.toList());
}

这种方法参考称为"对特定对象的实例方法的引用".在这种情况下，您指的是实例 this 的方法 createSomeValue.

This kind of method reference is called "Reference to an instance method of a particular object". In this case, you are referring to the method createSomeValue of the instance this.

使用 lambda 表达式是否更好"是一个见仁见智的问题.但是，您可以参考 this answer/brian-goetz">Brian Goetz 解释了为什么首先在语言中添加方法引用.

Whether it is "better" or not that using a lambda expression is a matter of opinion. However, you can refer to this answer written by Brian Goetz that explains why method-references were added in the language in the first place.