在java8中，如何在lambdas foreach块中设置全局值? [英] In java8, how to set the global value in the lambdas foreach block?

问题描述

    public void test(){
       String x;
       List<String> list=Arrays.asList("a","b","c","d");

       list.forEach(n->{
          if(n.equals("d"))
            x="match the value";
       });
    }

1.像上面的代码，我想在foreach块旁边设置一个变量的值，可以吗?

1.Like the code above, I want to set the value of a variable beside the foreach block, can it works?

2.为什么?

3.foreach迭代器是有序还是无序?

3.And the foreach iterator is in order or disorder?

4.我认为 lamdas foreach 块对于迭代器来说很酷也很简单，但这确实是一件很复杂的事情，而不是在 Java 7 或更早版本中进行相同的工作.

4.I think the lamdas foreach block is cool and simple for iterator,but this is really a complicated thing to do rather than the same work in java 7 or before.

推荐答案

当然，您可以通过一个技巧使外部值可变":

You could, of course, "make the outer value mutable" via a trick:

public void test() {
    String[] x = new String[1];
    List<String> list = Arrays.asList("a", "b", "c", "d");

    list.forEach(n -> {
        if (n.equals("d"))
            x[0] = "match the value";
    });
}

不过，准备好迎接团队中功能纯粹主义者的殴打.然而，更好的是使用更实用的方法(类似于 Sleiman 的方法):

Get ready for a beating by the functional purist on the team, though. Much nicer, however, is to use a more functional approach (similar to Sleiman's approach):

public void test() {
    List<String> list = Arrays.asList("a", "b", "c", "d");
    String x = list.stream()
                   .filter("d"::equals)
                   .findAny()
                   .map(v -> "match the value")
                   .orElse(null);
}

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