JShell で Effectively Final 遊び

Main.java

import java.util.Collections;
import java.util.List;
import java.util.stream.Stream;

/**
 * こんなつぶやきを見かけたので、debugオプションつけて雰囲気見てみたお話。
 * https://twitter.com/mike_neck/status/976358507011178496
 *
 * jshell> var list = List.of("foo", "bar")
 * list ==> [foo, bar]
 *
 * jshell> Stream.of("baz").forEach(s -> list = Collections.singletonList(s))
 *
 * jshell> list
 * list ==> [baz]
 */
public class Main {

  public static void main(String[] args) {
    System.out.println($JShell$12.do_it$());
    System.out.println($JShell$17.do_it$());
    System.out.println($JShell$21.do_it$());
  }

}

class $JShell$12 {
  public static List<String> list;

  public static Object do_it$() {
    List<String> list_ =
        List.of("foo", "bar");
    return list = list_;
  }
}

class $JShell$17 {
  public static Object do_it$() {
    Stream.of("baz").forEach(s -> $JShell$12.list = Collections.singletonList(s));
    return null;
  }
}

class $JShell$21 {
  public static Object do_it$() {
    return $JShell$12.list;
  }
}

[foo, bar]
null
[baz]

Process finished with exit code 0