[英]Remove certain elements in one list based on condition from another list
I'm fairly new to Java8.我是 Java8 的新手。 I have a requirement to subtract/remove POJOs in one list based on certain criteria (from another list) and show it on UI.
我需要根据特定条件(从另一个列表)减去/删除一个列表中的 POJO,并将其显示在 UI 上。
Iterate one list and search for condition Remove the object Send the original list to UI迭代一个列表并搜索条件 移除对象 将原始列表发送到 UI
Children.java
private String firstName;
private String lastName;
private String school;
private String personId;
// Setters and getters.
Person.java
private String personId;
private String fullName;
private String address;
// Setters and Getters.
..MAIN CODE.. ..主要代码..
// populated by other methods.
List<Person> personList;
//Connect to DB and get ChildrenList
List<Children> childrenList = criteria.list();
for(Children child : childrenList) {
personList.removeIf(person -> child.getPersonId().equals(person.getPersonId()));
}
Is there any BETTER way to HANDLE for-loop?有没有更好的方法来处理 for 循环? Any help is appreciated.
任何帮助表示赞赏。
The code that you have right now works perfectly, but is also O(n * m)
since removeIf
iterates through the List
for every Children
.您现在拥有的代码可以完美运行,但也是
O(n * m)
因为removeIf
遍历每个Children
的List
。 One way to improve would be to store every child's personId
in a Set<String>
and remove every Person
from the List<Person>
if their personId
is contained in the Set
:一种改进方法是将每个孩子的
personId
存储在Set<String>
中,如果personId
包含在Set
中,则从List<Person>
Person
删除每个人:
Set<String> childIds = childrenList.stream()
.map(Children::getPersonId)
.collect(Collectors.toSet());
personList.removeIf(person -> childIds.contains(person.getPersonId()));
Just another way of doing same but without mutating the original list:只是另一种做同样但不改变原始列表的方法:
Set<String> childIds = childrenList.stream()
.map(Children::getPersonId)
.collect(Collectors.toSet());
personList = personList.stream().filter(person ->
!childIds.contains(person.getPersonId())
).collect(Collectors.toList());
It should have a bit of increased space complexity but you could take advantage of parallelStream
here.它应该会增加一些空间复杂性,但您可以在这里利用
parallelStream
。
Adding this here in case someone needs it;在这里添加这个以防有人需要它;
If what you want to do is not checking the contents, but an equalization, you can do the same code as follows;如果你想做的不是检查内容,而是均衡,你可以做同样的代码如下;
listName.removeIf(listItem -> listItem.getName().equalsIgnoreCase("Name") ||
listItem.getName().equalsIgnoreCase("Other Name"));
This code is versatile and saved me lines of code and the need for a forEach loop.这段代码用途广泛,节省了我的代码行和 forEach 循环的需要。
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