Java 8中方法引用的外部参数 [英] External argument to method reference in Java 8

问题描述

我希望将外部参数传递给方法引用：

I am looking to pass an external parameter to a method reference:

String prefix = "The number is :";
numbers.forEach(Main::printWithPrefix);

private static void printWithPrefix(Integer number) {
    System.out.println(number);
}

我不知道如何做到这一点。我可以用lambda做到这一点：

I am no idea on how to do it. I am able to do it with a lambda:

String prefix = "The number is :";
numbers.forEach(number -> {
    System.out.println(prefix + number);
});

是否可以将外部参数传递给方法参考？

Is it possible to pass an external parameter to a method reference?

推荐答案

不，您不能将参数传递给方法参考。你可以做的是创建一个返回消费者的方法：

No, you cannot pass a parameter to a method reference. What you can do is create a method which returns a Consumer:

private static Consumer<Integer> printWithPrefix(String prefix) {
    return number -> System.out.println(prefix + number);
}

这可以作为创建消费者的工厂您可以传递给 numbers.forEach ：

This then works as a factory for creating a Consumer that you can pass to numbers.forEach:

String prefix = "The number is :";
numbers.forEach(printWithPrefix(prefix));

你甚至可以让它更通用一点，创建一个 printWithPrefix 将 Consumer 作为参数的方法，以便您可以传入不同的方法：

You can even make it a bit more general, creating a printWithPrefix method that takes a Consumer as an argument so that you could pass in a different one if you'd want to:

private static Consumer<Integer> printWithPrefix(String prefix,
                                                 Consumer<Integer> printer) {
    return number -> {
        System.out.print(prefix);
        printer.accept(number);
    };
}

你可以使用它，例如， printNumber 方法：

You could use it, for example, with a printNumber method:

private static void printNumber(Integer number) {
    System.out.println(number);
}

String prefix = "The number is :";
numbers.forEach(printWithPrefix(prefix, Main::printNumber));

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