Java 是否有可用于任何 lambda 的无操作 (NOP) 的方法参考？
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Is there a method reference for a no-op (NOP) that can be used for anything lambda?
提问by Ben
This may sounds like a strange question, but is there a way to refer to a standard no-op (aka null operation, null-pattern method, no-operation, do-nothing method) method for a Lambda in Java 8.
这听起来可能是一个奇怪的问题，但是有没有办法在 Java 8 中引用 Lambda 的标准无操作（又名空操作、空模式方法、无操作、无操作方法）方法。
Currently, I have a method that takes a, say, void foo(Consumer<Object>), and I want to give it a no-op, I have to declare:
目前，我有一个方法，比如，，void foo(Consumer<Object>)我想给它一个空操作，我必须声明：
foo(new Consumer<Object>() {
public void accept(Object o) {
// do nothing
}
}
where I would like to be able to do something like:
我希望能够执行以下操作：
foo(Object::null)
instead. Does something like exist?
反而。类似的东西存在吗？
Not sure how that would work with multi-parameter methods -- perhaps this is a deficiency in the lambdas in Java.
不确定这将如何与多参数方法一起使用——也许这是 Java 中 lambdas 的一个缺陷。
采纳答案by fge
This is no deficiency.
这不是不足。
Lambdas in Java are instances of functional interfaces; which, in turn, are abstracted to instances of Java constructs which can be simplified to onesingle abstract method, or SAM.
Java 中的 Lambda 是函数式接口的实例；反过来，它们又被抽象为 Java 结构的实例，这些实例可以简化为一个单一的抽象方法或 SAM。
But this SAM still needs to have a valid prototype. In your case, you want to have a no-op Consumer<T>which does nothing whatever the T.
但是这个SAM仍然需要有一个有效的原型。在您的情况下，您希望有一个无操作Consumer<T>，无论T.
It still needs to be a Consumer<T>however; which means the minimal declaration you can come up with is:
Consumer<T>然而，它仍然需要是一个；这意味着您可以提出的最小声明是：
private static final Consumer<Object> NOOP = whatever -> {};
and use NOOPwhere you need to.
并NOOP在需要的地方使用。
回答by Anderson Vieira
In your particular case you could simply do:
在您的特定情况下，您可以简单地执行以下操作：
foo(i -> {});
This means that the lambda expression receives a parameter but has no return value.
这意味着 lambda 表达式接收一个参数但没有返回值。
回答by OldCurmudgeon
Could Function.identity()fit your needs?
能Function.identity()满足你的需求吗？
Returns a function that always returns its input argument.
返回一个始终返回其输入参数的函数。
回答by Paul Boddington
If you want a method reference for a method that does nothing, the easiest way is to write a method that does nothing. Notice that in this example I have used Main::doNothingwhen a Consumer<String>is required.
如果你想要一个什么都不做的方法的方法引用，最简单的方法是编写一个什么都不做的方法。请注意，在此示例中，我使用了Main::doNothingwhen aConsumer<String>是必需的。
class Main {
static void doNothing(Object o) { }
static void foo(Consumer<String> c) { }
public static void main(String[] args) {
foo(Main::doNothing);
}
}
You could also overload doNothingby providing a version using varargs.
您还可以doNothing通过使用可变参数提供版本来重载。
static void doNothing(Object... o) { }
This signature will accept literally any sequence of parameters (even primitives, as these will get autoboxed). That way you could pass Main::doNothingwhenever the functional interface's method has voidreturn type. For example you could pass Main::doNothingwhen an ObjLongConsumer<Integer>is needed.
这个签名将接受任何参数序列（甚至是基元，因为它们会被自动装箱）。这样你就可以Main::doNothing在函数接口的方法有void返回类型时传递。例如，您可以Main::doNothing在ObjLongConsumer<Integer>需要时通过。
回答by MNZ
You can have your own NOOP implementation, similar to Function.Identity.
您可以拥有自己的 NOOP 实现，类似于 Function.Identity。
static <T> Consumer<T> NOOP() {
return t -> {};
}
