Sample code to convert List to List <String> in Java Stream

//Class of elements to put in List
public class MyData {

  public final String name;
  public final Integer age;

  public MyData(String name, Integer age) {
    this.name = name;
    this.age = age;
  }

  public String getMyInfo() {
    return name + "(" + age + ")";
  }
}

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;

public class Main {

  public static void main(String[] args) {

    //Build data
    List<MyData> list = new ArrayList<>() {
      {
        add(new MyData("Alice", 88));
        add(new MyData("Bob", 8));
        add(new MyData("Carol", null));
        add(null);
      }
    };

    //Conversion example 1
    List<String> list1 = list.stream() //Create Stream object
      .filter(Objects::nonNull)        //Exclude null elements
      .map(MyData::getMyInfo)          //Generate a string for each element
      .collect(Collectors.toList());   //List
    System.out.println(String.join("\n", list1));

    //Conversion example 2
    List<String> list2 = list.stream()                //Create Stream object
      .filter(Objects::nonNull)                       //Exclude null elements
      .map(mydata -> mydata.name + ": " + mydata.age) //Generate a string for each element
      .collect(Collectors.toList());                  //List
    System.out.println(String.join("\n", list2));

    //Conversion example 3
    List<String> list3 = list.stream() //Create Stream object
      .filter(Objects::nonNull)        //Exclude null elements
      .map(mydata -> {                 //Generate a string for each element
        if (mydata.age == null) {
          return mydata.name;
        } else {
          return mydata.name + ": " + mydata.age;
        }
      })
      .collect(Collectors.toList());   //List
    System.out.println(String.join("\n", list3));
  }
}

$ javac *.java
$ java Main
Alice(88)
Bob(8)
Carol(null)
Alice: 88
Bob: 8
Carol: null
Alice: 88
Bob: 8
Carol

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