Java 8 Stream – Convert List<List<String>> to List<String>
As title, we can use flatMap to convert it.
Java9Example1.java
package com.mkyong.test;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
import java.util.stream.Collectors;
public class Java9Example1 {
public static void main(String[] args) {
List<String> numbers = Arrays.asList("1", "2", "A", "B", "C1D2E3");
List<List<String>> collect = numbers.stream()
.map(x -> new Scanner(x).findAll("\\D+")
.map(m -> m.group())
.collect(Collectors.toList())
)
.collect(Collectors.toList());
collect.forEach(x -> System.out.println(x));
}
}
Output
[]
[]
[A]
[B]
[C, D, E]
Solution
Java9Example2.java
package com.mkyong.test;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
import java.util.stream.Collectors;
public class Java9Example2 {
public static void main(String[] args) {
List<String> numbers = Arrays.asList("1", "2", "A", "B", "C1D2E3");
List<String> collect = numbers.stream()
.map(x -> new Scanner(x).findAll("\\D+")
.map(m -> m.group())
.collect(Collectors.toList())
) // List<List<String>>
.flatMap(List::stream) // List<String>
.collect(Collectors.toList());
collect.forEach(x -> System.out.println(x));
}
}
Output
A
B
C
D
E
References
About Author
Founder of Mkyong.com, love Java and open source stuff. Follow him on Twitter. If you like my tutorials, consider make a donation to these charities.
I have a list of object . inside that list one more list of object . I required get one value of a variable as comma separated string i tried as below but i am getting error can help
String comaSepString =outerList.stream()
.collect(Collectors.toList()).stream().map(p->p.getMessage()).collect(Collectors.joining(“,”)) ;
Your comments that say List and List<String> should really say Stream and Stream<String>, I think. They only convert to List after the call to collect(…)
Ah, can’t get the formatting correct for the angle brackets to display, but I think the intention is clear…
I guess this example to Convert List to List . Can you update title?
“Java 8 Stream – Convert List to List” ?
The title is correct, this convert List List String to List String. Btw, what make you think so?
good job
I was confused with Input ( List numbers) List . You are correct .