Question

How to convert a List of Lists into a List in Java

Answer 1

import java.util.List;
import java.util.ArrayList;
import java.util.stream.Collectors;
 
public class MyClass {
    public static void main(String args[]) {
        List<List<String>> listOfLists = new ArrayList<>();
        
        List<String> innerList1 = new ArrayList<>();
        
        innerList1.add("Java");
        innerList1.add("Python");
        innerList1.add("Go");
        
        listOfLists.add(innerList1);
        
        List<String> innerList2 = new ArrayList<>();
        
        innerList2.add("C");
        innerList2.add("C#");
        innerList2.add("C++");
        innerList2.add("Rust");
        
        listOfLists.add(innerList2);  
        
        List<String> flattenedList = listOfLists.stream()
                                    .flatMap(List::stream)
                                    .collect(Collectors.toList());

        System.out.println(listOfLists);
        System.out.println(flattenedList);
    }
}
   
   
   
   
/*
run:
   
[[Java, Python, Go], [C, C#, C++, Rust]]
[Java, Python, Go, C, C#, C++, Rust]
  
*/

 

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