英文:
How to add a set of values from an ArrayList to another ArrayList using Lambda expression
问题
private List<MyObject> getObjectList(List<OtherObject> objects) {
List<MyObject> resultList = objects.stream()
.map(otherObject -> {
MyObject object = new MyObject();
object.setId(otherObject.getId());
object.setText(otherObject.getTextValue());
object.setUserId(otherObject.getUserName());
object.setCreatedDate(otherObject.getCreateDateTime());
return object;
})
.collect(Collectors.toList());
return resultList;
}
英文:
I have to create a result list by adding objects from one array list to another. Here is my code that works.
private List<MyObject> getObjectList(List<OtherObject> objects) {
List<MyObject> resultList = new ArrayList<>();
for (int i = 0; i < objects.size(); i++) {
MyObject object = new MyObject()
object.setId(objects.get(i).getId());
object.setText(objects.get(i).getTextValue());
object.setUserId(objects.get(i).getUserName());
object.setCreatedDate(objects.get(i).getCreateDateTime());
resultList.add(object);
}
return resultList;
}
How can I achieve this by using lambda expression?
答案1
得分: 3
这是使用方法引用的方法：
private List<MyObject> getObjectList(List<OtherObject> objects) {
return objects.stream()
.map(this::map)
.collect(Collectors.toList());
}
private MyObject map(OtherObject otherObject) {
MyObject object = new MyObject();
object.setId(otherObject.getId());
object.setText(otherObject.getTextValue());
object.setUserId(otherObject.getUserName());
object.setCreatedDate(otherObject.getCreateDateTime());
return object;
}
这是使用流和 Lambda 表达式的方法：
private List<MyObject> getObjectList(List<OtherObject> objects) {
return objects.stream()
.map(obj -> {
MyObject object = new MyObject();
object.setId(obj.getId());
object.setText(obj.getTextValue());
object.setUserId(obj.getUserName());
object.setCreatedDate(obj.getCreateDateTime());
return object;
}).collect(Collectors.toList());
}
英文:
Here's how you can do it with a method reference:
private List<MyObject> getObjectList(List<OtherObject> objects) {
return objects.stream()
.map(this::map)
.collect(Collectors.toList());
}
private MyObject map(OtherObject otherObject) {
MyObject object = new MyObject();
object.setId(otherObject.getId());
object.setText(otherObject.getTextValue());
object.setUserId(otherObject.getUserName());
object.setCreatedDate(otherObject.getCreateDateTime());
return object;
}
Here's how you can do it using streams and lambda expression:
private List<MyObject> getObjectList(List<OtherObject> objects) {
return objects.stream()
.map(obj -> {
MyObject object = new MyObject();
object.setId(obj.getId());
object.setText(obj.getTextValue());
object.setUserId(obj.getUserName());
object.setCreatedDate(obj.getCreateDateTime());
return object;
}).collect(Collectors.toList());
}
答案2
得分: 1
以下是一个示例：
private List<MyObject> getObjectList(List<OtherObject> objects) {
List<MyObject> resultList = new ArrayList<>();
objects.forEach(obj -> {
MyObject object = new MyObject();
object.setId(obj.getId());
object.setText(obj.getTextValue());
object.setUserId(obj.getUserName());
object.setCreatedDate(obj.getCreateDateTime());
resultList.add(object);
});
return resultList;
}
英文:
Here is an example:
private List<MyObject> getObjectList(List<OtherObject> objects) {
List<MyObject> resultList = new ArrayList<>();
objects.forEach(obj -> {
MyObject object = new MyObject();
object.setId(obj.getId());
object.setText(obj.getTextValue());
object.setUserId(obj.getUserName());
object.setCreatedDate(obj.getCreateDateTime());
resultList.add(object);
});
return resultList;
}
答案3
得分: 0
使用 [Record][1]
与你的 `OtherObject` 等效
```java
import java.time.LocalDateTime;
public record OtherRec(int id,
String textValue,
String userName,
LocalDateTime createDateTime) {
}
与你的 MyObject 等效
import java.time.LocalDateTime;
public record MyRecord(int id,
String text,
String userId,
LocalDateTime createDate) {
}
将 OtherRec 列表复制到 MyRecord
import java.time.LocalDateTime;
import java.util.List;
import java.util.stream.Collectors;
public class CopyList {
public static void main(String[] args) {
List<OtherRec> source = List.of(new OtherRec(1, "First", "One", LocalDateTime.of(2020, 10, 5, 12, 0)),
new OtherRec(2, "Second", "Two", LocalDateTime.of(2020, 10, 5, 13, 0)));
List<MyRecord> target = source.stream()
.map(or -> new MyRecord(or.id(), or.textValue(), or.userName(), or.createDateTime()))
.collect(Collectors.toList());
System.out.println(target);
}
}
<details>
<summary>英文:</summary>
Using [Record][1]
Equivalent of your `OtherObject`
```java
import java.time.LocalDateTime;
public record OtherRec(int id,
String textValue,
String userName,
LocalDateTime createDateTime) {
}
Equivalent of your MyObject
import java.time.LocalDateTime;
public record MyRecord(int id,
String text,
String userId,
LocalDateTime createDate) {
}
Copying list of OtherRec to MyRecord
import java.time.LocalDateTime;
import java.util.List;
import java.util.stream.Collectors;
public class CopyList {
public static void main(String[] args) {
List<OtherRec> source = List.of(new OtherRec(1, "First", "One", LocalDateTime.of(2020, 10, 5, 12, 0)),
new OtherRec(2, "Second", "Two", LocalDateTime.of(2020, 10, 5, 13, 0)));
List<MyRecord> target = source.stream()
.map(or -> new MyRecord(or.id(), or.textValue(), or.userName(), or.createDateTime()))
.collect(Collectors.toList());
System.out.println(target);
}
}
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