Chaining lambda functions [duplicate]

Question

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.

However, I'm wondering if there's a way to chain multiple method calls. Here's an example to illustrate the case.

// 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:

// something like: (which doesn't work)
String::trim::toUpperCase

Alternatively, is there a utility class to merge functions?

// example: (which does not exist)
FunctionUtil.chain(String::trim, String::toUpperCase);

Answer 1

Java 8 Functions can be chained with the method 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::trim does not compile because the trim method does not take any input, so it does not conform to the functional interface Function (same goes for String::toUpperCase).