问题

I've been using the java 8 Streams for a while. I came across a situation where I need to stream through a List and pass each element to a static method along with another argument. Is it possible in java 8?

........
String designation = "Engineer";
List<String> names = new ArrayList<>();
names.add("ABC");
names.add("DEF");
names.add("GHI");
names.stream().map(MyClass::createReport);
..........

class MyClass {
    public static void createReport(String name, String designation) {
       System.out.println(name+"\t"+designation);
    }
}

How can I pass the designation String via stream().map()?

回答1:

Use a lambda expression:

names.stream().map(name -> MyClass.createReport(name,designation))...

回答2:

You could write a curried version of the method createReport.

Curried `createReport`

We need to swap the order of the arguments because the designation for each name is the same. Additionly we just need to call the not curried method.

Function<String, Consumer<String>> createReportCurry = (designation) -> (name) -> {
    createReport(name, designation);
};

In Action

names.stream().forEach(createReportCurry.apply(designation))

回答3:

You could also use the following as an alternative:

IntStream.range(0, names.size())
         .forEach(i -> MyClass.createReport(names.get(i), names.get(i)));

回答4:

The above answer are very good but let's try to explain why you couldn't run your code in the first place:

Your code:

names.stream().map(MyClass::createReport);names.stream().map(MyClass::createReport);

What the JVM undertands

names.stream().map(MyClass::createReport);names.stream().map(name -> MyClass.createReport(name));

Solutions use a basic lamba as @Eran or a Function as @Roman suggested.

来源：https://stackoverflow.com/questions/53541030/java-8-calling-a-multi-argument-method-from-collection-stream-map

标签

java

lambda

java-8

java-stream

Java 8 - Calling a multi argument method from Collection.stream.map()

问题