嵌套在Java 8中的forEach [英] Nested forEach in Java 8

问题描述

我想用Java 8的流重写这段代码

I want to rewrite this piece of code in terms of streams from Java 8

for (Medium medium : sortierteMedien) {
    System.out.println("Fuenf aehnlichste Medien fuer " + medium.getClass() + " mit dem Titel " + medium.getTitel() + ":\n");


    for (Medium medium1 : bibliothek.medienSim(medium)) {
        System.out.println(medium1.toString());
    }

    System.out.println();
}

这里的困难在于，每个内部for循环前后都有一个print语句.

The difficulty here is, that there is a print statement before and after each inner for loop.

是否可以用流重写此内容?

Is it possible to rewrite this with streams?

推荐答案

循环内的强制性语句不是Stream API使用的典型任务.您仍然可以在不使用Stream API的情况下使用lambda表达式来执行此操作，即

Imperative statements within loops aren’t typical tasks for Stream API use. You still could do this using lambda expressions without the Stream API, i.e.

sortierteMedien.forEach(medium -> {
    System.out.println("Fuenf aehnlichste Medien fuer "
        +medium.getClass()+" mit dem Titel "+medium.getTitel()+":\n");
    bibliothek.medienSim(medium).forEach(System.out::println);
    System.out.println();
});

如果要在打印之前将所有内容收集到一个String中，那将是另一回事:

It would be a different thing, if you want to collect everything into one String before printing:

String result = sortierteMedien.stream().flatMap(medium -> Stream.concat(
        Stream.of("Fuenf aehnlichste Medien fuer "
            +medium.getClass()+" mit dem Titel "+medium.getTitel()+":\n"),
        bibliothek.medienSim(medium).stream().map(Medium::toString)
    ))
    .collect(Collectors.joining("\n"));
System.out.println(result);

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