使用 Lambda 的 Java 8 过滤器数组
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Java 8 Filter Array Using Lambda
提问by Makoto
I have a double[]and I want to filter out (create a new array without) negative values in one line without adding forloops. Is this possible using Java 8 lambda expressions?
我有一个double[]，我想在一行中过滤掉（创建一个没有新数组）负值而不添加for循环。这可以使用 Java 8 lambda 表达式吗？
In python it would be this using generators:
在 python 中，这将是使用生成器：
[i for i in x if i > 0]
Is it possible to do something similarly concise in Java 8?
是否有可能在 Java 8 中做一些类似的简洁的事情？
采纳答案by Alex
Yes, you can do this by creating a DoubleStreamfrom the array, filtering out the negatives, and converting the stream back to an array. Here is an example:
是的，您可以通过DoubleStream从数组中创建 a 、过滤掉负数并将流转换回数组来实现这一点。下面是一个例子：
double[] d = {8, 7, -6, 5, -4};
d = Arrays.stream(d).filter(x -> x > 0).toArray();
//d => [8, 7, 5]
If you want to filter a reference array that is not an Object[]you will need to use the toArraymethod which takes an IntFunctionto get an array of the original type as the result:
如果你想过滤一个不是 an 的引用数组，Object[]你需要使用一个toArray方法IntFunction来获取一个原始类型的数组作为结果：
String[] a = { "s", "", "1", "", "" };
a = Arrays.stream(a).filter(s -> !s.isEmpty()).toArray(String[]::new);
回答by keypoint
even simpler, adding up to String[],
甚至更简单，加起来String[]，
use built-in filter filter(StringUtils::isNotEmpty)of org.apache.commons.lang3
使用内置过滤器filter(StringUtils::isNotEmpty)的org.apache.commons.lang3
import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.StringUtils;
String test = "a\nb\n\nc\n";
String[] lines = test.split("\n", -1);
String[] result = Arrays.stream(lines).filter(StringUtils::isNotEmpty).toArray(String[]::new);
System.out.println(Arrays.toString(lines));
System.out.println(Arrays.toString(result));
and output:
[a, b, , c, ]
[a, b, c]
和输出：
[a, b, , c, ]
[a, b, c]
