从Java 8流中断或返回每个? [英] Break or return from Java 8 stream forEach?
问题描述
在 Iterable
上使用外部迭代时,我们使用 break
或<$ c从增强型for-each循环返回$ c> return :
When using external iteration over an Iterable
we use break
or return
from enhanced for-each loop as:
for (SomeObject obj : someObjects) {
if (some_condition_met) {
break; // or return obj
}
}
我们如何 break
或使用Java 8 lambda表达式中的内部迭代返回
,如:
How can we break
or return
using the internal iteration in a Java 8 lambda expression like:
someObjects.forEach(obj -> {
//what to do here?
})
推荐答案
如果你需要这个,你不应该使用 forEach
,但是流上可用的其他方法之一;哪一个,取决于你的目标是什么。
If you need this, you shouldn't use forEach
, but one of the other methods available on streams; which one, depends on what your goal is.
例如,如果这个循环的目标是找到匹配某个谓词的第一个元素:
For example, if the goal of this loop is to find the first element which matches some predicate:
Optional<SomeObject> result =
someObjects.stream().filter(obj -> some_condition_met).findFirst();
(注意:这不会迭代整个集合,因为流被懒惰评估 - 它将停在匹配条件的第一个对象。)
(Note: This will not iterate the whole collection, because streams are lazily evaluated - it will stop at the first object that matches the condition).
如果你只是想知道条件为真的集合中是否有一个元素,你可以使用 anyMatch
:
If you just want to know if there's an element in the collection for which the condition is true, you could use anyMatch
:
boolean result = someObjects.stream().anyMatch(obj -> some_condition_met);
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