java 链接 lambda 函数
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Chaining lambda functions
提问by bvdb
When a Java method accepts a Function<? super T, ? extends U>, then it's possible to provide method references in a syntax like the following: MyClass::myMethod.
当 Java 方法接受 a 时Function<? super T, ? extends U>，可以使用如下语法提供方法引用：MyClass::myMethod.
However, I'm wondering if there's a way to chain multiple method calls. Here's an example to illustrate the case.
但是，我想知道是否有一种方法可以链接多个方法调用。这里有一个例子来说明这种情况。
// on a specific object, without lambda
myString.trim().toUpperCase()
I am wondering if there is a syntax to translate this to a lambda expression. I am hoping there is something like the following:
我想知道是否有将其转换为 lambda 表达式的语法。我希望有如下内容：
// something like: (which doesn't work)
String::trim::toUpperCase
Alternatively, is there a utility class to merge functions?
或者，是否有用于合并函数的实用程序类？
// example: (which does not exist)
FunctionUtil.chain(String::trim, String::toUpperCase);
采纳答案by Tunaki
Java 8 Functions can be chained with the method andThen:
Java 8Function可以使用以下方法链接andThen：
UnaryOperator<String> trimFunction = String::trim;
UnaryOperator<String> toUpperCaseFunction = String::toUpperCase;
Stream.of(" a ", " b ").map(trimFunction.andThen(toUpperCaseFunction)) // Stream is now ["A", "B"]
Note that in your actual example, String::trimdoes not compile because the trimmethod does not take any input, so it does not conform to the functional interface Function(same goes for String::toUpperCase).
请注意，在您的实际示例中，String::trim不会编译，因为该trim方法不接受任何输入，因此它不符合功能接口Function（同样适用于String::toUpperCase）。
