从 Java 8 中的方法返回 Lambda？
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Return Lambda from Method in Java 8?
提问by Philip Lombardi
I have just begun to use Java 8 and I am wondering if there is a way to write a method that returns a Function?
我刚刚开始使用 Java 8，我想知道是否有一种方法可以编写一个返回Function?
Right now I have method like below:
现在我有如下方法：
Function<Integer, String> getMyFunction() {
return new Function<Integer, String>() {
@Override public String apply(Integer integer) {
return "Hello, world!"
}
}
}
Is there a way to write that more succinctly in Java 8? I was hoping this would work but it does not:
有没有办法在 Java 8 中更简洁地编写它？我希望这会起作用，但它不起作用：
Function<Integer, String> getMyFunction() {
return (it) -> { return "Hello, world: " + it }
}
采纳答案by mkobit
Get rid of your return statement inside of your function definition:
去掉函数定义中的 return 语句：
Function<Integer, String> getMyFunction() {
return (it) -> "Hello, world: " + it;
}
回答by assylias
You are missing semi colons:
您缺少分号：
return (it) -> { return "Hello, world: " + it; };
Although as noted it can be shortened to:
虽然如前所述，它可以缩短为：
return it -> "Hello, world: " + it;
回答by Oussama Zoghlami
You could write it simply like that:
你可以简单地这样写：
Function<Integer, String> function = n -> "Hello, world " + n;
回答by Jo?o Antunes
So, the answer for 99% of the cases has been given by @assylias
所以，@assylias 已经给出了 99% 的答案
You are missing semi colons:
return (it) -> { return "Hello, world: " + it; }; Although as noted itcan be shortened to:
return it -> "Hello, world: " + it;
您缺少分号：
return (it) -> { return "Hello, world: " + it; }; Although as noted it可以缩短为：
return it -> "Hello, world: " + it;
Yet, I think that it's worth it to add that, if you want to assign your lambda to a variable (to use later). You can do so by typing:
但是，如果您想将 lambda 分配给变量（稍后使用），我认为值得添加这一点。您可以通过键入：
Callable<YourClass> findIt = () -> returnInstanceOfYourClass();
And then you can easily use it, one example of such a use:
然后你就可以很容易地使用它了，一个这样使用的例子：
if(dontNeedzToWrap()) {
return findIt.call();
}
return Wrapp.withTransaction(() -> findIt.call());
Given, things can be even made simpler if the Wrapp.withTransaction()method accepts the same kind of Callable's as parameters.
(I use this for JPA atm)
鉴于，如果该Wrapp.withTransaction()方法接受相同类型的 Callable 作为参数，事情甚至可以变得更简单。（我将此用于 JPA atm）
回答by Magnilex
I would like to point out that it might be more appropriate to use the built-in IntFunctionin this case:
我想指出，IntFunction在这种情况下使用内置函数可能更合适：
IntFunction<String> getMyFunction() {
return it -> "Hello, world: " + it;
}
IntFunctionis a part of the standard API for functional interfaceswhich defines a range of good to have interfaces, mostly related to Java primitives.
