Java 8 - 如何使用带参数函数的谓词? [英] Java 8 - How to use predicate that has a function with parameter?
问题描述
我有以下代码:
public boolean isImageSrcExists(String imageSrc) {
int resultsNum = 0;
List<WebElement> blogImagesList = driver.findElements(blogImageLocator);
for (WebElement thisImage : blogImagesList) {
if (thisImage.getAttribute("style").contains(imageSrc)) {
resultsNum++;
}
}
if (resultsNum == 2) {
return true;
} else {
return false;
}
}
将其转换为使用Java的正确方法是什么8 流
s?
What is the proper way of converting it to use Java 8 Stream
s?
当我尝试使用 map()
,我收到错误,因为 getAttribute
不是函数
。
When I'm trying to use map()
, I get an error since getAttribute
isn't a Function
.
int a = (int) blogImagesList.stream()
.map(WebElement::getAttribute("style"))
.filter(s -> s.contains(imageSrc))
.count();
推荐答案
你无法做到你想要的 - 显式参数是方法引用中不允许。
You cannot do exactly what you want - explicit parameters are not allowed in method references.
但是你可以......
But you could...
...创建一个返回的方法布尔和编码调用 getAttribute(style)
:
...create a method that returns a boolean and harcoded the call to getAttribute("style")
:
public boolean getAttribute(final T t) {
return t.getAttribute("style");
}
这将允许您使用方法ref:
This would allow you to use the method ref:
int a = (int) blogImagesList.stream()
.map(this::getAttribute)
.filter(s -> s.contains(imageSrc))
.count();
...或者您可以定义一个变量来保存该函数:
...or you could define a variable to hold the function:
final Function<T, R> mapper = t -> t.getAttribute("style");
这将允许您简单地传递变量
This would allow you to simply pass the variable
int a = (int) blogImagesList.stream()
.map(mapper)
.filter(s -> s.contains(imageSrc))
.count();
...或者你可以讨论并结合上述两种方法(这肯定是可怕的过度杀伤)
...or you could curry and combine the above two approaches (this is certainly horribly overkill)
public Function<T,R> toAttributeExtractor(String attrName) {
return t -> t.getAttribute(attrName);
}
然后你需要调用 toAttributeExtractor
获取功能
并将其传递到地图
:
Then you would need to call toAttributeExtractor
to get a Function
and pass that into the map
:
final Function<T, R> mapper = toAttributeExtractor("style");
int a = (int) blogImagesList.stream()
.map(mapper)
.filter(s -> s.contains(imageSrc))
.count();
虽然实际上,简单地使用lambda会更容易(就像你在下一行一样):
Although, realistically, simply using a lambda would be easier (as you do on the next line):
int a = (int) blogImagesList.stream()
.map(t -> t.getAttribute("style"))
.filter(s -> s.contains(imageSrc))
.count();
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