[PATCH] 8247402: Rewrite the implementation requirements for Map::compute()

[Martin Buchholz]

林自均, pleased to meet you!

This rewrite seems clear and clean.

Would it be even clearer if we did

if (newValue != null) {
  map.put(key, newValue);
} else {
  map.remove(key);
}

Hmmm, what about the corner case where the map permits null values and
the old value is null?

On Thu, Jun 11, 2020 at 7:45 PM 林自均 <johnlinp at gmail.com> wrote:
>
> Hi all,
>
> This is my first time contribution. Please let me know if I did
> something wrong. Thanks. Regards
>
> I'm working on this bug: https://bugs.openjdk.java.net/browse/JDK-8247402
>
> The original problem is that the implementation requirements for
> Map::compute() lacks of return statements for some cases. However, I
> found that there are some other problems in it:
>
> 1. The indents are 3 spaces, while most of the indents are 4 spaces.
> 2. The if-else is overly complicated and can be simplified.
>
> My proposed patch that generated by `hg export -g` is:
>
> # HG changeset patch
> # User John Lin <johnlinp at gmail.com>
> # Date 1591923561 -28800
> #      Fri Jun 12 08:59:21 2020 +0800
> # Node ID 03c9b5c9e632a0d6e33a1f13c98bb3b31b1bf659
> # Parent  49a68abdb0ba68351db0f140ddac793b1c391bd5
> 8247402: Rewrite the implementation requirements for Map::compute()
>
> diff --git a/src/java.base/share/classes/java/util/Map.java
> b/src/java.base/share/classes/java/util/Map.java
> --- a/src/java.base/share/classes/java/util/Map.java
> +++ b/src/java.base/share/classes/java/util/Map.java
> @@ -1113,17 +1113,12 @@ public interface Map<K, V> {
>       * <pre> {@code
>       * V oldValue = map.get(key);
>       * V newValue = remappingFunction.apply(key, oldValue);
> -     * if (oldValue != null) {
> -     *    if (newValue != null)
> -     *       map.put(key, newValue);
> -     *    else
> -     *       map.remove(key);
> -     * } else {
> -     *    if (newValue != null)
> -     *       map.put(key, newValue);
> -     *    else
> -     *       return null;
> +     * if (newValue != null) {
> +     *     map.put(key, newValue);
> +     * } else if (oldValue != null) {
> +     *     map.remove(key);
>       * }
> +     * return newValue;
>       * }</pre>
>       *
>       * <p>The default implementation makes no guarantees about detecting if the
>
> Best,
> John Lin