Java 8:方法引用绑定接收器和未绑定接收器的区别 [英] Java 8: Difference between method reference Bound Receiver and UnBound Receiver

问题描述

我正在尝试在我的代码中使用 Java 8 方法引用.有四种类型的方法引用可用.

I am trying to use Java 8 method references in my code. There are four types of method references available.

1. 静态方法参考.
2. 实例方法(绑定接收器).
3. 实例方法(未绑定接收器).
4. 构造函数参考.

使用 Static method reference 和 Constructor reference 我没有问题，但是 Instance Method (Bound receiver) 和 Instance Method (未绑定的接收器) 真的让我很困惑.在 Bound 接收器中，我们使用对象引用变量来调用如下方法:

With Static method reference and Constructor reference i have no problem, but Instance Method (Bound receiver) and Instance Method (UnBound receiver) really confused me. In Bound receiver, we are using an Object reference variable for calling a method like:

objectRef::Instance Method

在 UnBound 接收器中，我们使用类名来调用如下方法:

In UnBound receiver we are using Class name for calling a method like:

ClassName::Instance Method.

我有以下问题:

1. 不同类型的实例方法需要什么方法引用?
2. Bound 和 Unbound 接收器方法引用有什么区别?
3. 我们应该在哪里使用 Bound 接收器，我们应该在哪里使用 Unbound 接收器?

1. What is the need for different types of method references for Instance Methods?
2. What is the difference between Bound and Unbound receiver method references?
3. Where should we use Bound receiver and where should we use Unbound receiver?

我还从 Java 8 语言特性书籍，但仍然与实际概念混淆.

I also found the explanation of Bound and Unbound receiver from Java 8 language features books, but was still confused with the actual concept.

推荐答案

像 String::length 这样的 unBound 接收器的想法是你指的是将作为 lambda 参数之一提供的对象的方法.例如，lambda 表达式 (String s) ->s.toUpperCase() 可以改写为 String::toUpperCase.

The idea of the unBound receiver such as String::length is you're referring to a method of an object that will be supplied as one of the lambda's parameters. For example, the lambda expression (String s) -> s.toUpperCase() can be rewritten as String::toUpperCase.

但是有界是指当你在一个方法中调用一个方法时的情况lambda 到一个已经存在的外部对象.例如，lambda 表达式 () ->priceTransaction.getValue() 可以改写为 expensiveTransaction::getValue.

But Bounded refers to a situation when you’re calling a method in a lambda to an external object that already exists. For example, the lambda expression () -> expensiveTransaction.getValue() can be rewritten as expensiveTransaction::getValue.

三种不同的方法引用方式的情况

Situations for three different ways of method reference

(args) ->ClassName.staticMethod(args)可以是 ClassName::staticMethod//这是静态的(你也可以认为是 unBound)

(args) -> ClassName.staticMethod(args) can be ClassName::staticMethod // This is static (you can think as unBound also)

(arg0, rest) ->arg0.instanceMethod(rest)可以是 ClassName::instanceMethod (arg0 is of type ClassName)//这是未绑定的

(arg0, rest) -> arg0.instanceMethod(rest) can be ClassName::instanceMethod (arg0 is of type ClassName) // This is unBound

(args) ->expr.instanceMethod(args)可以是 expr::instanceMethod//这是绑定的

(args) -> expr.instanceMethod(args) can be expr::instanceMethod // This is Bound

从Java 8 in Action 书中检索的答案

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