I was trying to run the below code

import java.util.Arrays;
import java.util.List;

class HelloWorld {
    
    
    public static void main(String[] args){
    ttt();
  }

  public static void ttt(){
      
    List<String> result;
    result = kkk();
    // String ll = result.get(0);
    // ll.split(",");
    if(result.get(0) instanceof String){
      System.out.println("alsfjalsdfjaslkfj");
    }else{
      System.out.println("Long Long");

    }
    System.out.println(result);
  }

  public static <R> R kkk(){
    List<Long> x = Arrays.asList(2L, 2L, 3L);
    return (R) x;
  }
}

I was expecting the code to fail at compile time. Surprisingly, the code runs printing “Long Long”. How is Java able to load List<Long> into List<String>. Is there any documentation about this behaviour?