Java - 使用条件和 Lambda 在数组中查找元素
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Java - Find Element in Array using Condition and Lambda
提问by Joe Almore
In short, I have this code, and I'd like to get an specific element of the array using a condition and lambda. The code would be something like this:
简而言之，我有这段代码，我想使用条件和 lambda 来获取数组的特定元素。代码将是这样的：
Preset[] presets = presetDALC.getList();
Preset preset = Arrays.stream(presets).select(x -> x.getName().equals("MyString"));
But obviously this does not work. In C# would be something similar but in Java, how do I do this?
但显然这行不通。在 C# 中会类似，但在 Java 中，我该怎么做？
采纳答案by CoderCroc
You can do it like this,
你可以这样做，
Optional<Preset> optional = Arrays.stream(presets)
.filter(x -> "MyString".equals(x.getName()))
.findFirst();
if(optional.isPresent()) {//Check whether optional has element you are looking for
Preset p = optional.get();//get it from optional
}
You can read more about Optionalhere.
您可以Optional在此处阅读更多信息。
回答by Robby Cornelissen
Like this:
像这样：
Optional<Preset> preset = Arrays
.stream(presets)
.filter(x -> x.getName().equals("MyString"))
.findFirst();
This will return an Optionalwhich might or might not contain a value. If you want to get rid of the Optionalaltogether:
这将返回一个Optional可能包含也可能不包含值的 。如果你想Optional完全摆脱：
Preset preset = Arrays
.stream(presets)
.filter(x -> x.getName().equals("MyString"))
.findFirst()
.orElse(null);
The filter()operation is an intermediate operation which returns a lazy stream, so there's no need to worry about the entire array being filtered even after a match is encountered.
该filter()操作是一个返回惰性流的中间操作，因此即使遇到匹配项，也无需担心整个数组会被过滤。
回答by Andreas
Do you want first matching, or all matching?
你是要先匹配还是全部匹配？
String[] presets = {"A", "B", "C", "D", "CA"};
// Find all matching
List<String> resultList = Arrays.stream(presets)
.filter(x -> x.startsWith("C"))
.collect(Collectors.toList());
System.out.println(resultList);
// Find first matching
String firstResult = Arrays.stream(presets)
.filter(x -> x.startsWith("C"))
.findFirst()
.orElse(null);
System.out.println(firstResult);
Output
输出
[C, CA]
C
