Java 8修改流元素 [英] Java 8 modify stream elements
问题描述
我想用Java 8编写纯函数,该函数将集合作为参数,对集合的每个对象进行一些更改,并在更新后返回一个新集合.我想遵循FP原则,所以我不想更新/修改作为参数传递的集合.
I wanted to write pure function with Java 8 that would take a collection as an argument, apply some change to every object of that collection and return a new collection after the update. I want to follow FP principles so I dont want to update/modify the collection that was passed as an argument.
是否可以通过Stream API进行任何操作而无需先创建原始集合的副本(然后使用forEach或"normal"的for循环)?
Is there any way of doing that with Stream API without creating a copy of the original collection first (and then using forEach or 'normal' for loop)?
在下面对对象进行采样,并假设我想将文本附加到对象属性之一:
Sample object below and lets assume that I want to append a text to one of the object property:
public class SampleDTO {
private String text;
}
所以我想做类似下面的事情,但不修改集合.假设列表"是List<SampleDTO>
.
So I want to do something similar to below, but without modifying the collection. Assuming "list" is a List<SampleDTO>
.
list.forEach(s -> {
s.setText(s.getText()+"xxx");
});
推荐答案
您必须具有一些生成现有SampleDTO
实例副本的方法/构造函数,例如副本构造函数.
You must have some method/constructor that generates a copy of an existing SampleDTO
instance, such as a copy constructor.
然后,您可以将每个原始SampleDTO
实例map
变为一个新的SampleDTO
实例,并将它们collect
变为一个新的List
:
Then you can map
each original SampleDTO
instance to a new SampleDTO
instance, and collect
them into a new List
:
List<SampleDTO> output =
list.stream()
.map(s-> {
SampleDTO n = new SampleDTO(s); // create new instance
n.setText(n.getText()+"xxx"); // mutate its state
return n; // return mutated instance
})
.collect(Collectors.toList());
这篇关于Java 8修改流元素的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!